diff --git a/docs/source/extending.rst b/docs/source/extending.rst
index 8dc4313f..c8f01e7a 100644
--- a/docs/source/extending.rst
+++ b/docs/source/extending.rst
@@ -74,9 +74,9 @@ atom object called ``SimpleAtom`` that has attributes ``x``, ``y`` and ``z``.
             zpar = ParameterAdapter("z", atom, attr = "z")
 
             # Add these to the parameter set
-            self.addParameter(xpar)
-            self.addParameter(ypar)
-            self.addParameter(zpar)
+            self.add_parameter(xpar)
+            self.add_parameter(ypar)
+            self.add_parameter(zpar)
 
             return
 
@@ -85,7 +85,7 @@ atom object called ``SimpleAtom`` that has attributes ``x``, ``y`` and ``z``.
 The ``x``, ``y`` and ``z`` attributes (specified by the ``attr`` keyword
 argument of ``ParameterAdapter``) of a ``SimpleAtom`` are wrapped as
 ``ParameterAdapter`` objects named `x`, `y`, and `z`.  They are then added to
-the ``SimpleAtomParSet`` using the ``addParameter`` method, which makes them
+the ``SimpleAtomParSet`` using the ``add_parameter`` method, which makes them
 accessible as attributes.
 
 If SimpleAtom did not have an attribute named ``x``, but rather accessor
diff --git a/news/addparameter-dep.rst b/news/addparameter-dep.rst
new file mode 100644
index 00000000..631d9877
--- /dev/null
+++ b/news/addparameter-dep.rst
@@ -0,0 +1,26 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* ``ParameterSet.addParameter``, ``ParameterSet.newParameter`` and
+  ``ParameterSet.removeParameter`` are deprecated in favour of
+  ``add_parameter``, ``new_parameter`` and ``remove_parameter``. The old names
+  still work and warn, and will be removed in version 4.0.0.
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>
diff --git a/src/diffpy/srfit/fitbase/fitcontribution.py b/src/diffpy/srfit/fitbase/fitcontribution.py
index d896e86e..d135205d 100644
--- a/src/diffpy/srfit/fitbase/fitcontribution.py
+++ b/src/diffpy/srfit/fitbase/fitcontribution.py
@@ -196,9 +196,9 @@ def set_profile(self, profile, xname=None, yname=None, dyname=None):
         xpar = ParameterProxy(xname, self.profile.xpar)
         ypar = ParameterProxy(yname, self.profile.ypar)
         dypar = ParameterProxy(dyname, self.profile.dypar)
-        self.addParameter(xpar, check=False)
-        self.addParameter(ypar, check=False)
-        self.addParameter(dypar, check=False)
+        self.add_parameter(xpar, check=False)
+        self.add_parameter(ypar, check=False)
+        self.add_parameter(dypar, check=False)
 
         # If we have ProfileGenerators, set their Profiles.
         for gen in self._generators.values():
@@ -290,7 +290,7 @@ def set_equation(self, eqstr, ns={}):
         ----------
         eqstr : str
             A string representation of the equation. Any Parameter
-            registered by ``addParameter`` or ``set_profile``, or function
+            registered by ``add_parameter`` or ``set_profile``, or function
             registered by ``register_calculator``, ``register_function`` or
             ``register_string_function`` can be used in the equation
             by name. Other names will be turned into Parameters of this
diff --git a/src/diffpy/srfit/fitbase/parameterset.py b/src/diffpy/srfit/fitbase/parameterset.py
index 21bb2dac..3c031596 100644
--- a/src/diffpy/srfit/fitbase/parameterset.py
+++ b/src/diffpy/srfit/fitbase/parameterset.py
@@ -34,6 +34,18 @@
     base, "addParameterSet", "add_parameter_set", removal_version
 )
 
+addParameter_dep_msg = build_deprecation_message(
+    base, "addParameter", "add_parameter", removal_version
+)
+
+newParameter_dep_msg = build_deprecation_message(
+    base, "newParameter", "new_parameter", removal_version
+)
+
+removeParameter_dep_msg = build_deprecation_message(
+    base, "removeParameter", "remove_parameter", removal_version
+)
+
 removeParameterSet_dep_msg = build_deprecation_message(
     base, "removeParameterSet", "remove_parameter_set", removal_version
 )
@@ -99,9 +111,42 @@ def __init__(self, name):
         return
 
     # Alias Parameter accessors.
-    addParameter = RecipeOrganizer._add_parameter
-    newParameter = RecipeOrganizer._new_parameter
-    removeParameter = RecipeOrganizer._remove_parameter
+    add_parameter = RecipeOrganizer._add_parameter
+    new_parameter = RecipeOrganizer._new_parameter
+    remove_parameter = RecipeOrganizer._remove_parameter
+
+    @deprecated(addParameter_dep_msg)
+    def addParameter(self, parameter, check=True):
+        """This function has been deprecated and will be removed in version
+        4.0.0.
+
+        Please use
+        diffpy.srfit.fitbase.parameterset.ParameterSet.add_parameter
+        instead.
+        """
+        return self.add_parameter(parameter, check)
+
+    @deprecated(newParameter_dep_msg)
+    def newParameter(self, name, value, check=True):
+        """This function has been deprecated and will be removed in version
+        4.0.0.
+
+        Please use
+        diffpy.srfit.fitbase.parameterset.ParameterSet.new_parameter
+        instead.
+        """
+        return self.new_parameter(name, value, check)
+
+    @deprecated(removeParameter_dep_msg)
+    def removeParameter(self, parameter):
+        """This function has been deprecated and will be removed in version
+        4.0.0.
+
+        Please use
+        diffpy.srfit.fitbase.parameterset.ParameterSet.remove_parameter
+        instead.
+        """
+        return self.remove_parameter(parameter)
 
     def add_parameter_set(self, parset):
         """Add a ParameterSet to the hierarchy.
diff --git a/src/diffpy/srfit/fitbase/profilegenerator.py b/src/diffpy/srfit/fitbase/profilegenerator.py
index 2b642289..2093931a 100644
--- a/src/diffpy/srfit/fitbase/profilegenerator.py
+++ b/src/diffpy/srfit/fitbase/profilegenerator.py
@@ -29,9 +29,9 @@ def __init__(self):
             # Initialize and give this a name
             ProfileGenerator.__init__(self, "g")
             # Add amplitude, center and width parameters
-            self.newParameter("amp", 0)
-            self.newParameter("center", 0)
-            self.newParameter("width", 0)
+            self.new_parameter("amp", 0)
+            self.new_parameter("center", 0)
+            self.new_parameter("width", 0)
         def __call__(self, x):
             a = self.amp.getValue()
             x0 = self.center.getValue()
diff --git a/src/diffpy/srfit/pdf/basepdfgenerator.py b/src/diffpy/srfit/pdf/basepdfgenerator.py
index 0c4d7341..6d546da8 100644
--- a/src/diffpy/srfit/pdf/basepdfgenerator.py
+++ b/src/diffpy/srfit/pdf/basepdfgenerator.py
@@ -122,7 +122,7 @@ def _set_calculator(self, calc):
         """
         self._calc = calc
         for pname in self.__class__._parnames:
-            self.addParameter(ParameterAdapter(pname, self._calc, attr=pname))
+            self.add_parameter(ParameterAdapter(pname, self._calc, attr=pname))
         self._process_metadata()
         return
 
diff --git a/src/diffpy/srfit/pdf/characteristicfunctions.py b/src/diffpy/srfit/pdf/characteristicfunctions.py
index 4e760538..1acc5921 100644
--- a/src/diffpy/srfit/pdf/characteristicfunctions.py
+++ b/src/diffpy/srfit/pdf/characteristicfunctions.py
@@ -654,14 +654,14 @@ def __init__(self, name, model):
         # Wrap normal parameters
         for parname in model.params:
             par = SASParameter(parname, model)
-            self.addParameter(par)
+            self.add_parameter(par)
 
         # Wrap dispersion parameters
         for parname in model.dispersion:
             name = parname + "_width"
             parname += ".width"
             par = SASParameter(name, model, parname)
-            self.addParameter(par)
+            self.add_parameter(par)
 
         return
 
diff --git a/src/diffpy/srfit/pdf/pdfcontribution.py b/src/diffpy/srfit/pdf/pdfcontribution.py
index b103a414..dc54adb3 100644
--- a/src/diffpy/srfit/pdf/pdfcontribution.py
+++ b/src/diffpy/srfit/pdf/pdfcontribution.py
@@ -96,10 +96,10 @@ def __init__(self, name):
 
         # Need a parameter for the overall scale, in the case that this is a
         # multi-phase fit.
-        self.newParameter("scale", 1.0)
+        self.new_parameter("scale", 1.0)
         # Profile-related parameters that will be shared between the generators
-        self.newParameter("qdamp", 0)
-        self.newParameter("qbroad", 0)
+        self.new_parameter("qdamp", 0)
+        self.new_parameter("qbroad", 0)
         return
 
     # Data methods
diff --git a/src/diffpy/srfit/sas/sasgenerator.py b/src/diffpy/srfit/sas/sasgenerator.py
index a986e283..df3024aa 100644
--- a/src/diffpy/srfit/sas/sasgenerator.py
+++ b/src/diffpy/srfit/sas/sasgenerator.py
@@ -57,14 +57,14 @@ def __init__(self, name, model):
         # Wrap normal parameters
         for parname in model.params:
             par = SASParameter(parname, model)
-            self.addParameter(par)
+            self.add_parameter(par)
 
         # Wrap dispersion parameters
         for parname in model.dispersion:
             name = parname + "_width"
             parname += ".width"
             par = SASParameter(name, model, parname)
-            self.addParameter(par)
+            self.add_parameter(par)
 
         return
 
diff --git a/src/diffpy/srfit/structure/cctbxparset.py b/src/diffpy/srfit/structure/cctbxparset.py
index 99711c07..d2c89023 100644
--- a/src/diffpy/srfit/structure/cctbxparset.py
+++ b/src/diffpy/srfit/structure/cctbxparset.py
@@ -70,19 +70,19 @@ def __init__(self, name, strups, idx):
         self.idx = idx
 
         # x, y, z, occupancy
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("x", None, self._xyzgetter(0), self._xyzsetter(0))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("y", None, self._xyzgetter(1), self._xyzsetter(1))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("z", None, self._xyzgetter(2), self._xyzsetter(2))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("occupancy", None, self._getocc, self._setocc)
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("Uiso", None, self._getuiso, self._setuiso)
         )
         return
@@ -163,26 +163,26 @@ def __init__(self, strups):
         self.strups = strups
         self._latpars = list(self.strups.stru.unit_cell().parameters())
 
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("a", None, self._latgetter(0), self._latsetter(0))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("b", None, self._latgetter(1), self._latsetter(1))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("c", None, self._latgetter(2), self._latsetter(2))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter(
                 "alpha", None, self._latgetter(3), self._latsetter(3)
             )
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter(
                 "beta", None, self._latgetter(4), self._latsetter(4)
             )
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter(
                 "gamma", None, self._latgetter(5), self._latsetter(5)
             )
diff --git a/src/diffpy/srfit/structure/diffpyparset.py b/src/diffpy/srfit/structure/diffpyparset.py
index 545cb976..6d2d17b6 100644
--- a/src/diffpy/srfit/structure/diffpyparset.py
+++ b/src/diffpy/srfit/structure/diffpyparset.py
@@ -102,52 +102,52 @@ def __init__(self, name, atom):
         self.atom = atom
         a = atom
         # x, y, z, occupancy
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("x", a, _xyzgetter(0), _xyzsetter(0))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("y", a, _xyzgetter(1), _xyzsetter(1))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("z", a, _xyzgetter(2), _xyzsetter(2))
         )
         occupancy = ParameterAdapter("occupancy", a, attr="occupancy")
-        self.addParameter(occupancy)
-        self.addParameter(ParameterProxy("occ", occupancy))
+        self.add_parameter(occupancy)
+        self.add_parameter(ParameterProxy("occ", occupancy))
         # U
-        self.addParameter(ParameterAdapter("U11", a, attr="U11"))
-        self.addParameter(ParameterAdapter("U22", a, attr="U22"))
-        self.addParameter(ParameterAdapter("U33", a, attr="U33"))
+        self.add_parameter(ParameterAdapter("U11", a, attr="U11"))
+        self.add_parameter(ParameterAdapter("U22", a, attr="U22"))
+        self.add_parameter(ParameterAdapter("U33", a, attr="U33"))
         U12 = ParameterAdapter("U12", a, attr="U12")
         U21 = ParameterProxy("U21", U12)
         U13 = ParameterAdapter("U13", a, attr="U13")
         U31 = ParameterProxy("U31", U13)
         U23 = ParameterAdapter("U23", a, attr="U23")
         U32 = ParameterProxy("U32", U23)
-        self.addParameter(U12)
-        self.addParameter(U21)
-        self.addParameter(U13)
-        self.addParameter(U31)
-        self.addParameter(U23)
-        self.addParameter(U32)
-        self.addParameter(ParameterAdapter("Uiso", a, attr="Uisoequiv"))
+        self.add_parameter(U12)
+        self.add_parameter(U21)
+        self.add_parameter(U13)
+        self.add_parameter(U31)
+        self.add_parameter(U23)
+        self.add_parameter(U32)
+        self.add_parameter(ParameterAdapter("Uiso", a, attr="Uisoequiv"))
         # B
-        self.addParameter(ParameterAdapter("B11", a, attr="B11"))
-        self.addParameter(ParameterAdapter("B22", a, attr="B22"))
-        self.addParameter(ParameterAdapter("B33", a, attr="B33"))
+        self.add_parameter(ParameterAdapter("B11", a, attr="B11"))
+        self.add_parameter(ParameterAdapter("B22", a, attr="B22"))
+        self.add_parameter(ParameterAdapter("B33", a, attr="B33"))
         B12 = ParameterAdapter("B12", a, attr="B12")
         B21 = ParameterProxy("B21", B12)
         B13 = ParameterAdapter("B13", a, attr="B13")
         B31 = ParameterProxy("B31", B13)
         B23 = ParameterAdapter("B23", a, attr="B23")
         B32 = ParameterProxy("B32", B23)
-        self.addParameter(B12)
-        self.addParameter(B21)
-        self.addParameter(B13)
-        self.addParameter(B31)
-        self.addParameter(B23)
-        self.addParameter(B32)
-        self.addParameter(ParameterAdapter("Biso", a, attr="Bisoequiv"))
+        self.add_parameter(B12)
+        self.add_parameter(B21)
+        self.add_parameter(B13)
+        self.add_parameter(B31)
+        self.add_parameter(B23)
+        self.add_parameter(B32)
+        self.add_parameter(ParameterAdapter("Biso", a, attr="Bisoequiv"))
         return
 
     def __repr__(self):
@@ -216,26 +216,26 @@ def __init__(self, lattice):
         self.angunits = "deg"
         self.lattice = lattice
         lat = lattice
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("a", lat, _latgetter("a"), _latsetter("a"))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("b", lat, _latgetter("b"), _latsetter("b"))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter("c", lat, _latgetter("c"), _latsetter("c"))
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter(
                 "alpha", lat, _latgetter("alpha"), _latsetter("alpha")
             )
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter(
                 "beta", lat, _latgetter("beta"), _latsetter("beta")
             )
         )
-        self.addParameter(
+        self.add_parameter(
             ParameterAdapter(
                 "gamma", lat, _latgetter("gamma"), _latsetter("gamma")
             )
diff --git a/src/diffpy/srfit/structure/objcrystparset.py b/src/diffpy/srfit/structure/objcrystparset.py
index 755f818e..22e9ec08 100644
--- a/src/diffpy/srfit/structure/objcrystparset.py
+++ b/src/diffpy/srfit/structure/objcrystparset.py
@@ -130,10 +130,12 @@ def __init__(self, name, scat, parent):
         self.parent = parent
 
         # x, y, z, occ
-        self.addParameter(ParameterAdapter("x", self.scat, attr="X"))
-        self.addParameter(ParameterAdapter("y", self.scat, attr="Y"))
-        self.addParameter(ParameterAdapter("z", self.scat, attr="Z"))
-        self.addParameter(ParameterAdapter("occ", self.scat, attr="Occupancy"))
+        self.add_parameter(ParameterAdapter("x", self.scat, attr="X"))
+        self.add_parameter(ParameterAdapter("y", self.scat, attr="Y"))
+        self.add_parameter(ParameterAdapter("z", self.scat, attr="Z"))
+        self.add_parameter(
+            ParameterAdapter("occ", self.scat, attr="Occupancy")
+        )
         return
 
     def isDummy(self):
@@ -191,22 +193,22 @@ def __init__(self, name, atom, parent):
         sp = atom.GetScatteringPower()
 
         # The B-parameters
-        self.addParameter(ParameterAdapter("Biso", sp, attr="Biso"))
-        self.addParameter(ParameterAdapter("B11", sp, attr="B11"))
-        self.addParameter(ParameterAdapter("B22", sp, attr="B22"))
-        self.addParameter(ParameterAdapter("B33", sp, attr="B33"))
+        self.add_parameter(ParameterAdapter("Biso", sp, attr="Biso"))
+        self.add_parameter(ParameterAdapter("B11", sp, attr="B11"))
+        self.add_parameter(ParameterAdapter("B22", sp, attr="B22"))
+        self.add_parameter(ParameterAdapter("B33", sp, attr="B33"))
         B12 = ParameterAdapter("B12", sp, attr="B12")
         B21 = ParameterProxy("B21", B12)
         B13 = ParameterAdapter("B13", sp, attr="B13")
         B31 = ParameterProxy("B31", B13)
         B23 = ParameterAdapter("B23", sp, attr="B23")
         B32 = ParameterProxy("B32", B23)
-        self.addParameter(B12)
-        self.addParameter(B21)
-        self.addParameter(B13)
-        self.addParameter(B31)
-        self.addParameter(B23)
-        self.addParameter(B32)
+        self.add_parameter(B12)
+        self.add_parameter(B21)
+        self.add_parameter(B13)
+        self.add_parameter(B31)
+        self.add_parameter(B23)
+        self.add_parameter(B32)
 
         # Give a value to Biso if it doesn't have one, and this is isotropic
         if sp.IsIsotropic() and self.Biso.value == 0:
@@ -267,10 +269,10 @@ def __init__(self, name, molecule, parent=None):
         self.stru = molecule
 
         # Add orientation quaternion
-        self.addParameter(ParameterAdapter("q0", self.scat, attr="Q0"))
-        self.addParameter(ParameterAdapter("q1", self.scat, attr="Q1"))
-        self.addParameter(ParameterAdapter("q2", self.scat, attr="Q2"))
-        self.addParameter(ParameterAdapter("q3", self.scat, attr="Q3"))
+        self.add_parameter(ParameterAdapter("q0", self.scat, attr="Q0"))
+        self.add_parameter(ParameterAdapter("q1", self.scat, attr="Q1"))
+        self.add_parameter(ParameterAdapter("q2", self.scat, attr="Q2"))
+        self.add_parameter(ParameterAdapter("q3", self.scat, attr="Q3"))
 
         # Wrap the MolAtoms within the molecule
         self.atoms = []
@@ -400,7 +402,7 @@ def wrapStretchModeParameters(self):
 
             par.AddAtoms(atoms)
 
-            self.addParameter(par)
+            self.add_parameter(par)
 
         for mode in self.scat.GetStretchModeBondAngleList():
             name1 = mode.mpAtom0.GetName()
@@ -423,7 +425,7 @@ def wrapStretchModeParameters(self):
                 atoms.append(getattr(self, name))
             par.AddAtoms(atoms)
 
-            self.addParameter(par)
+            self.add_parameter(par)
 
         return
 
@@ -686,7 +688,7 @@ def addBondLengthParameter(
             Returns the new ObjCrystBondLengthParameter.
         """
         par = ObjCrystBondLengthParameter(name, atom1, atom2, value, const)
-        self.addParameter(par)
+        self.add_parameter(par)
 
         return par
 
@@ -726,7 +728,7 @@ def addBondAngleParameter(
         par = ObjCrystBondAngleParameter(
             name, atom1, atom2, atom3, value, const
         )
-        self.addParameter(par)
+        self.add_parameter(par)
 
         return par
 
@@ -770,7 +772,7 @@ def addDihedralAngleParameter(
         par = ObjCrystDihedralAngleParameter(
             name, atom1, atom2, atom3, atom4, value, const
         )
-        self.addParameter(par)
+        self.add_parameter(par)
 
         return par
 
@@ -825,22 +827,22 @@ def __init__(self, name, scat, parent):
 
         # Only wrap this if there is a scattering power
         if sp is not None:
-            self.addParameter(ParameterAdapter("Biso", sp, attr="Biso"))
-            self.addParameter(ParameterAdapter("B11", sp, attr="B11"))
-            self.addParameter(ParameterAdapter("B22", sp, attr="B22"))
-            self.addParameter(ParameterAdapter("B33", sp, attr="B33"))
+            self.add_parameter(ParameterAdapter("Biso", sp, attr="Biso"))
+            self.add_parameter(ParameterAdapter("B11", sp, attr="B11"))
+            self.add_parameter(ParameterAdapter("B22", sp, attr="B22"))
+            self.add_parameter(ParameterAdapter("B33", sp, attr="B33"))
             B12 = ParameterAdapter("B12", sp, attr="B12")
             B21 = ParameterProxy("B21", B12)
             B13 = ParameterAdapter("B13", sp, attr="B13")
             B31 = ParameterProxy("B31", B13)
             B23 = ParameterAdapter("B23", sp, attr="B23")
             B32 = ParameterProxy("B32", B23)
-            self.addParameter(B12)
-            self.addParameter(B21)
-            self.addParameter(B13)
-            self.addParameter(B31)
-            self.addParameter(B23)
-            self.addParameter(B32)
+            self.add_parameter(B12)
+            self.add_parameter(B21)
+            self.add_parameter(B13)
+            self.add_parameter(B31)
+            self.add_parameter(B23)
+            self.add_parameter(B32)
 
         return
 
@@ -1817,12 +1819,12 @@ def __init__(self, name, cryst):
         self.stru = cryst
         self._sgpars = None
 
-        self.addParameter(ParameterAdapter("a", self.stru, attr="a"))
-        self.addParameter(ParameterAdapter("b", self.stru, attr="b"))
-        self.addParameter(ParameterAdapter("c", self.stru, attr="c"))
-        self.addParameter(ParameterAdapter("alpha", self.stru, attr="alpha"))
-        self.addParameter(ParameterAdapter("beta", self.stru, attr="beta"))
-        self.addParameter(ParameterAdapter("gamma", self.stru, attr="gamma"))
+        self.add_parameter(ParameterAdapter("a", self.stru, attr="a"))
+        self.add_parameter(ParameterAdapter("b", self.stru, attr="b"))
+        self.add_parameter(ParameterAdapter("c", self.stru, attr="c"))
+        self.add_parameter(ParameterAdapter("alpha", self.stru, attr="alpha"))
+        self.add_parameter(ParameterAdapter("beta", self.stru, attr="beta"))
+        self.add_parameter(ParameterAdapter("gamma", self.stru, attr="gamma"))
 
         # Now we must loop over the scatterers and create parameter sets from
         # them.
diff --git a/tests/test_contribution.py b/tests/test_contribution.py
index 56975905..6c2f3059 100644
--- a/tests/test_contribution.py
+++ b/tests/test_contribution.py
@@ -303,9 +303,9 @@ def test_setEquation(noObserversInGlobalBuilders):
     fc.setEquation("x + 5")
     fc.x.set_value(2)
     assert 7 == fc.evaluate()
-    fc.removeParameter(fc.x)
+    fc.remove_parameter(fc.x)
     x = arange(0, 10, 0.5)
-    fc.newParameter("x", x)
+    fc.new_parameter("x", x)
     assert np.array_equal(5 + x, fc.evaluate())
     assert noObserversInGlobalBuilders
     return
@@ -317,9 +317,9 @@ def test_set_equation(noObserversInGlobalBuilders):
     fc.set_equation("x + 5")
     fc.x.set_value(2)
     assert 7 == fc.evaluate()
-    fc.removeParameter(fc.x)
+    fc.remove_parameter(fc.x)
     x = arange(0, 10, 0.5)
-    fc.newParameter("x", x)
+    fc.new_parameter("x", x)
     assert np.array_equal(5 + x, fc.evaluate())
     assert noObserversInGlobalBuilders
     return
diff --git a/tests/test_parameterset.py b/tests/test_parameterset.py
index 1838c2f4..a1e15a30 100644
--- a/tests/test_parameterset.py
+++ b/tests/test_parameterset.py
@@ -14,8 +14,11 @@
 ##############################################################################
 """Tests for refinableobj module."""
 
+import re
 import unittest
 
+import pytest
+
 from diffpy.srfit.fitbase.parameter import Parameter
 from diffpy.srfit.fitbase.parameterset import ParameterSet
 
@@ -37,7 +40,7 @@ def test_add_parameter_set(self):
         self.assertRaises(ValueError, self.parset.add_parameter_set, p1)
 
         p1.name = "p1"
-        parset2.addParameter(p1)
+        parset2.add_parameter(p1)
 
         self.assertTrue(self.parset.parset2.p1 is p1)
 
@@ -70,12 +73,79 @@ def test_add_parameter_set_deprecated(self):
         self.assertRaises(ValueError, self.parset.add_parameter_set, p1)
 
         p1.name = "p1"
-        parset2.addParameter(p1)
+        parset2.add_parameter(p1)
 
         self.assertTrue(self.parset.parset2.p1 is p1)
 
         return
 
 
+# ----------------------------------------------------------------------------
+# The camelCase Parameter accessors on ParameterSet are deprecated in favour of
+# their snake_case spellings. Each old name must still work, warn with a
+# message that names its replacement, and have the same effect on the set.
+
+
+# C1: A Parameter is stored under the set with the deprecated name.
+# Expected: addParameter warns and stores it as add_parameter does.
+def test_add_parameter_deprecated():
+    expected_msg = (
+        "'diffpy.srfit.fitbase.parameterset.ParameterSet.addParameter' is "
+        "deprecated and will be removed in version 4.0.0. "
+        "Please use "
+        "'diffpy.srfit.fitbase.parameterset.ParameterSet.add_parameter' "
+        "instead."
+    )
+    expected_names = ["p1"]
+    parset = ParameterSet("test")
+
+    with pytest.warns(DeprecationWarning, match=re.escape(expected_msg)):
+        parset.addParameter(Parameter("p1", 1))
+
+    actual_names = [par.name for par in parset._parameters.values()]
+    assert actual_names == expected_names
+
+
+# C2: A Parameter is created and stored with the deprecated name.
+# Expected: newParameter warns and creates it as new_parameter does.
+def test_new_parameter_deprecated():
+    expected_msg = (
+        "'diffpy.srfit.fitbase.parameterset.ParameterSet.newParameter' is "
+        "deprecated and will be removed in version 4.0.0. "
+        "Please use "
+        "'diffpy.srfit.fitbase.parameterset.ParameterSet.new_parameter' "
+        "instead."
+    )
+    expected_names = ["p1"]
+    parset = ParameterSet("test")
+
+    with pytest.warns(DeprecationWarning, match=re.escape(expected_msg)):
+        parset.newParameter("p1", 1)
+
+    actual_names = [par.name for par in parset._parameters.values()]
+    assert actual_names == expected_names
+
+
+# C3: A stored Parameter is removed from the set with the deprecated name.
+# Expected: removeParameter warns and removes it as remove_parameter does.
+def test_remove_parameter_deprecated():
+    expected_msg = (
+        "'diffpy.srfit.fitbase.parameterset.ParameterSet.removeParameter' is "
+        "deprecated and will be removed in version 4.0.0. "
+        "Please use "
+        "'diffpy.srfit.fitbase.parameterset.ParameterSet.remove_parameter' "
+        "instead."
+    )
+    expected_names = []
+    parset = ParameterSet("test")
+    p1 = parset.new_parameter("p1", 1)
+
+    with pytest.warns(DeprecationWarning, match=re.escape(expected_msg)):
+        parset.removeParameter(p1)
+
+    actual_names = [par.name for par in parset._parameters.values()]
+    assert actual_names == expected_names
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/test_recipeorganizer.py b/tests/test_recipeorganizer.py
index 1b953c3b..193b35ed 100644
--- a/tests/test_recipeorganizer.py
+++ b/tests/test_recipeorganizer.py
@@ -190,7 +190,7 @@ def tearDown(self):
         return
 
     def testNewParameter(self):
-        """Test the addParameter method."""
+        """Test the add_parameter method."""
         m = self.m
 
         p1 = Parameter("p1", 1)
@@ -205,7 +205,7 @@ def testNewParameter(self):
         return
 
     def testAddParameter(self):
-        """Test the addParameter method."""
+        """Test the add_parameter method."""
         m = self.m
 
         p1 = Parameter("p1", 1)
@@ -242,7 +242,7 @@ def testAddParameter(self):
         return
 
     def testRemoveParameter(self):
-        """Test removeParameter method."""
+        """Test remove_parameter method."""
         m = self.m
 
         p1 = Parameter("p1", 1)
@@ -419,9 +419,9 @@ class GCalc(Calculator):
 
             def __init__(self, name):
                 Calculator.__init__(self, name)
-                self.newParameter("A", 1.0)
-                self.newParameter("center", 0.0)
-                self.newParameter("width", 0.1)
+                self.new_parameter("A", 1.0)
+                self.new_parameter("center", 0.0)
+                self.new_parameter("width", 0.1)
                 return
 
             def __call__(self, x):
@@ -464,9 +464,9 @@ class GCalc(Calculator):
 
             def __init__(self, name):
                 Calculator.__init__(self, name)
-                self.newParameter("A", 1.0)
-                self.newParameter("center", 0.0)
-                self.newParameter("width", 0.1)
+                self.new_parameter("A", 1.0)
+                self.new_parameter("center", 0.0)
+                self.new_parameter("width", 0.1)
                 return
 
             def __call__(self, x):
diff --git a/tests/test_weakrefcallable.py b/tests/test_weakrefcallable.py
index 688bc563..e6d58fa6 100644
--- a/tests/test_weakrefcallable.py
+++ b/tests/test_weakrefcallable.py
@@ -110,7 +110,7 @@ def test_pickling(self):
     def test_observable_deregistration(self):
         """Check if Observable drops dead Observer."""
         f = self.f
-        x = f.newParameter("x", 5)
+        x = f.new_parameter("x", 5)
         f.set_equation("3 * x")
         self.assertEqual(15, f.evaluate())
         self.assertEqual(15, f._eq._value)