diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3a82707..6498d73 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,13 @@ project adheres to clauses 1–8 of [Semantic Versioning](https://semver.org/spe
 
 ## [Unreleased]
 
+## [0.15.2] (Jun 28 2024)
+
+### Changed
+
+- `ParamDataFrame` now saves and loads DataFrames to and from Pickle files instead of CSV
+  files.
+
 ## [0.15.1] (Jun 26 2024)
 
 ### Fixed
diff --git a/paramdb/_param_data/_files.py b/paramdb/_param_data/_files.py
index 2e06c18..3ffeb2e 100644
--- a/paramdb/_param_data/_files.py
+++ b/paramdb/_param_data/_files.py
@@ -1,7 +1,7 @@
 """Base class for parameter files."""
 
 from __future__ import annotations
-from typing import TypeVar, Generic
+from typing import TypeVar, Generic, cast
 from abc import abstractmethod
 from dataclasses import InitVar
 from paramdb._param_data._dataclasses import ParamDataclass
@@ -68,12 +68,12 @@ class ParamDataFrame(ParamFile[pd.DataFrame]):
         """
         Subclass of :py:class:`ParamFile`.
 
-        Parameter data Pandas DataFrame, stored in a CSV file (with no index). This
-        class will only be defined if Pandas is installed.
+        Parameter data Pandas DataFrame, stored in a Pickle file. This class will only
+        be defined if Pandas is installed.
         """
 
         def _load_data(self, path: str) -> pd.DataFrame:
-            return pd.read_csv(path)
+            return cast(pd.DataFrame, pd.read_pickle(path))
 
         def _save_data(self, path: str, data: pd.DataFrame) -> None:
-            data.to_csv(path, index=False)
+            data.to_pickle(path)
diff --git a/tests/_param_data/test_files.py b/tests/_param_data/test_files.py
index 33ec86c..611cbaa 100644
--- a/tests/_param_data/test_files.py
+++ b/tests/_param_data/test_files.py
@@ -88,7 +88,7 @@ def test_param_file_saves_file(
     type(param_file)(param_file_path, data)
     assert os.path.exists(param_file_path)
     if isinstance(param_file, ParamDataFrame):
-        pd.testing.assert_frame_equal(data, pd.read_csv(param_file_path))
+        pd.testing.assert_frame_equal(data, pd.read_pickle(param_file_path))
     else:
         with open(param_file_path, "r", encoding="utf-8") as f:
             assert data == f.read()