diff --git a/gtsam/hybrid/GaussianMixture.cpp b/gtsam/hybrid/GaussianMixture.cpp
index f61b280cb..1913be7aa 100644
--- a/gtsam/hybrid/GaussianMixture.cpp
+++ b/gtsam/hybrid/GaussianMixture.cpp
@@ -298,9 +298,14 @@ double GaussianMixture::error(const HybridValues &values) const {
 
 /* *******************************************************************************/
 double GaussianMixture::logProbability(const HybridValues &values) const {
-  // Directly index to get the conditional, no need to build the whole tree.
   auto conditional = conditionals_(values.discrete());
   return conditional->logProbability(values.continuous());
 }
 
+/* *******************************************************************************/
+double GaussianMixture::evaluate(const HybridValues &values) const {
+  auto conditional = conditionals_(values.discrete());
+  return conditional->evaluate(values.continuous());
+}
+
 }  // namespace gtsam
diff --git a/gtsam/hybrid/GaussianMixture.h b/gtsam/hybrid/GaussianMixture.h
index a8d07cbc8..2137acff6 100644
--- a/gtsam/hybrid/GaussianMixture.h
+++ b/gtsam/hybrid/GaussianMixture.h
@@ -175,7 +175,7 @@ class GTSAM_EXPORT GaussianMixture
 
   /**
    * @brief Compute the error of this Gaussian Mixture.
-   * 
+   *
    * log(probability(x)) = K - error(x)
    *
    * @param values Continuous values and discrete assignment.
@@ -191,12 +191,13 @@ class GTSAM_EXPORT GaussianMixture
    */
   double logProbability(const HybridValues &values) const override;
 
-  //   /// Calculate probability density for given values `x`.
-  //   double evaluate(const HybridValues &values) const;
+  /// Calculate probability density for given `values`.
+  double evaluate(const HybridValues &values) const override;
 
-  //   /// Evaluate probability density, sugar.
-  //   double operator()(const HybridValues &values) const { return
-  //   evaluate(values); }
+  /// Evaluate probability density, sugar.
+  double operator()(const HybridValues &values) const {
+    return evaluate(values);
+  }
 
   /**
    * @brief Prune the decision tree of Gaussian factors as per the discrete
diff --git a/gtsam/hybrid/HybridConditional.cpp b/gtsam/hybrid/HybridConditional.cpp
index 55fd5d5d4..24f61a85f 100644
--- a/gtsam/hybrid/HybridConditional.cpp
+++ b/gtsam/hybrid/HybridConditional.cpp
@@ -151,4 +151,24 @@ double HybridConditional::logProbability(const HybridValues &values) const {
       "HybridConditional::logProbability: conditional type not handled");
 }
 
+/* ************************************************************************ */
+double HybridConditional::logNormalizationConstant() const {
+  if (auto gc = asGaussian()) {
+    return gc->logNormalizationConstant();
+  }
+  if (auto gm = asMixture()) {
+    return gm->logNormalizationConstant(); // 0.0!
+  }
+  if (auto dc = asDiscrete()) {
+    return dc->logNormalizationConstant(); // 0.0!
+  }
+  throw std::runtime_error(
+      "HybridConditional::logProbability: conditional type not handled");
+}
+
+/* ************************************************************************ */
+double HybridConditional::evaluate(const HybridValues &values) const {
+  return std::exp(logProbability(values));
+}
+
 }  // namespace gtsam
diff --git a/gtsam/hybrid/HybridConditional.h b/gtsam/hybrid/HybridConditional.h
index 19c070974..c8cb968df 100644
--- a/gtsam/hybrid/HybridConditional.h
+++ b/gtsam/hybrid/HybridConditional.h
@@ -179,9 +179,19 @@ class GTSAM_EXPORT HybridConditional
   /// Return the error of the underlying conditional.
   double error(const HybridValues& values) const override;
 
-  /// Return the logProbability of the underlying conditional.
+  /// Return the log-probability (or density) of the underlying conditional.
   double logProbability(const HybridValues& values) const override;
 
+  /**
+   * Return the log normalization constant.
+   * Note this is 0.0 for discrete and hybrid conditionals, but depends
+   * on the continuous parameters for Gaussian conditionals.
+   */ 
+  double logNormalizationConstant() const override;
+
+  /// Return the probability (or density) of the underlying conditional.
+  double evaluate(const HybridValues& values) const override;
+
   /// Check if VectorValues `measurements` contains all frontal keys.
   bool frontalsIn(const VectorValues& measurements) const {
     for (Key key : frontals()) {
diff --git a/gtsam/hybrid/tests/testHybridConditional.cpp b/gtsam/hybrid/tests/testHybridConditional.cpp
new file mode 100644
index 000000000..da766a56f
--- /dev/null
+++ b/gtsam/hybrid/tests/testHybridConditional.cpp
@@ -0,0 +1,75 @@
+/* ----------------------------------------------------------------------------
+
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation,
+ * Atlanta, Georgia 30332-0415
+ * All Rights Reserved
+ * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
+
+ * See LICENSE for the license information
+
+ * -------------------------------------------------------------------------- */
+
+/**
+ * @file    testHybridConditional.cpp
+ * @brief   Unit tests for HybridConditional class
+ * @date    January 2023
+ */
+
+#include <gtsam/hybrid/HybridConditional.h>
+
+#include "TinyHybridExample.h"
+
+// Include for test suite
+#include <CppUnitLite/TestHarness.h>
+
+using namespace gtsam;
+
+using symbol_shorthand::M;
+using symbol_shorthand::X;
+using symbol_shorthand::Z;
+
+/* ****************************************************************************/
+// Check invariants for all conditionals in a tiny Bayes net.
+TEST(HybridConditional, Invariants) {
+  // Create hybrid Bayes net p(z|x,m)p(x)P(m)
+  auto bn = tiny::createHybridBayesNet();
+
+  // Create values to check invariants.
+  const VectorValues c{{X(0), Vector1(5.1)}, {Z(0), Vector1(4.9)}};
+  const DiscreteValues d{{M(0), 1}};
+  const HybridValues values{c, d};
+
+  // Check invariants for p(z|x,m)
+  auto hc1 = bn.at(0);
+  CHECK(hc1->isHybrid());
+  GTSAM_PRINT(*hc1);
+
+  // Check invariants as a GaussianMixture.
+  const auto mixture = hc1->asMixture();
+  double probability = mixture->evaluate(values);
+  CHECK(probability >= 0.0);
+  EXPECT_DOUBLES_EQUAL(probability, (*mixture)(values), 1e-9);
+  double logProb = mixture->logProbability(values);
+  EXPECT_DOUBLES_EQUAL(probability, std::exp(logProb), 1e-9);
+  double expected =
+      mixture->logNormalizationConstant() - mixture->error(values);
+  EXPECT_DOUBLES_EQUAL(logProb, expected, 1e-9);
+  EXPECT(GaussianMixture::CheckInvariants(*mixture, values));
+
+  // Check invariants as a HybridConditional.
+  probability = hc1->evaluate(values);
+  CHECK(probability >= 0.0);
+  EXPECT_DOUBLES_EQUAL(probability, (*hc1)(values), 1e-9);
+  logProb = hc1->logProbability(values);
+  EXPECT_DOUBLES_EQUAL(probability, std::exp(logProb), 1e-9);
+  expected = hc1->logNormalizationConstant() - hc1->error(values);
+  EXPECT_DOUBLES_EQUAL(logProb, expected, 1e-9);
+  EXPECT(HybridConditional::CheckInvariants(*hc1, values));
+}
+
+/* ************************************************************************* */
+int main() {
+  TestResult tr;
+  return TestRegistry::runAllTests(tr);
+}
+/* ************************************************************************* */