diff --git a/ChangeLog b/ChangeLog
index 3a3f03f88..ef650cb37 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2010-03-08 Richard Frith-Macdonald <rfm@gnu.org>
+
+	* Source/NSObject.m:
+	* Source/Additions/GSObjCRuntime.m:
+	* Documentation/Base.gsdoc:
+	* Headers/Additions/GNUstepBase/GSObjCRuntime.h:
+	Add GNUSTEP_BEHAVIOR_DEBUG enovironment variable to turn on logging
+	of the use of behaviors/overrides of class methds by a list of
+	methods from another class.
+
 2010-03-08 Richard Frith-Macdonald <rfm@gnu.org>
 
 	* Source/GSArray.m: Re-remove [GSMutableArray count] (GSMutableArray
diff --git a/Documentation/Base.gsdoc b/Documentation/Base.gsdoc
index f180ad2ec..fabc89148 100644
--- a/Documentation/Base.gsdoc
+++ b/Documentation/Base.gsdoc
@@ -388,6 +388,13 @@ notice and this notice are preserved.
 		or you want to use an alternative config file for some reason.
 	      </p>
 	    </desc>
+	    <term>GNUSTEP_BEHAVIOR_DEBUG</term>
+	    <desc>
+	      A boolean (YES or NO) which can be used to turn on debug
+	      logging (to stderr) of the GSObjCRuntime functions to
+	      add/override methods in a class using a list of methods
+	      from another class.
+	    </desc>
 	    <term>HOMEDRIVE</term>
 	    <desc>
 	      <p>
diff --git a/Headers/Additions/GNUstepBase/GSObjCRuntime.h b/Headers/Additions/GNUstepBase/GSObjCRuntime.h
index 7401b28e3..d76e404d8 100644
--- a/Headers/Additions/GNUstepBase/GSObjCRuntime.h
+++ b/Headers/Additions/GNUstepBase/GSObjCRuntime.h
@@ -176,6 +176,10 @@ GSObjCAddClassBehavior(Class receiver, Class behavior);
 GS_EXPORT void
 GSObjCAddClassOverride(Class receiver, Class override);
 
+/** Turn on (YES), off (NO) or test (-1) behavior debugging.
+ */
+GS_EXPORT BOOL GSObjCBehaviorDebug(int setget);
+
 GS_EXPORT NSValue *
 GSObjCMakeClass(NSString *name, NSString *superName, NSDictionary *iVars);
 
diff --git a/Source/Additions/GSObjCRuntime.m b/Source/Additions/GSObjCRuntime.m
index a33a99d0c..2f218a4dd 100644
--- a/Source/Additions/GSObjCRuntime.m
+++ b/Source/Additions/GSObjCRuntime.m
@@ -477,24 +477,36 @@ GSObjCAddClasses(NSArray *classes)
 
 
 
-static int behavior_debug = 0;
+static BOOL behavior_debug = NO;
 
-void
+BOOL
 GSObjCBehaviorDebug(int i)
 {
-  behavior_debug = i;
+  BOOL	old = behavior_debug;
+
+  if (i == YES)
+    {
+      behavior_debug = YES;
+    }
+  else if (i == NO)
+    {
+      behavior_debug = NO;
+    }
+  return old;
 }
 
 void
 GSObjCAddMethods(Class cls, Method *list, BOOL replace)
 {
   unsigned int	index = 0;
+  char		c;
   Method	m;
 
   if (cls == 0 || list == 0)
     {
       return;
     }
+  c = class_isMetaClass(cls) ? '+' : '-';
 
   while ((m = list[index++]) != NULL)
     {
@@ -507,15 +519,19 @@ GSObjCAddMethods(Class cls, Method *list, BOOL replace)
        */
       if (YES == class_addMethod(cls, n, i, t))
 	{
-          BDBGPrintf("    added %s\n", sel_getName(n));
+          BDBGPrintf("    added %c%s\n", c, sel_getName(n));
 	}
       else if (YES == replace)
 	{
 	  /* If we want to replace an existing implemetation ...
 	   */
 	  method_setImplementation(class_getInstanceMethod(cls, n), i);
-          BDBGPrintf("    replaced %s\n", sel_getName(n));
+          BDBGPrintf("    replaced %c%s\n", c, sel_getName(n));
 	} 
+      else
+	{
+          BDBGPrintf("    skipped %c%s\n", c, sel_getName(n));
+	}
     }
 }
 
@@ -806,13 +822,13 @@ GSObjCAddClassBehavior(Class receiver, Class behavior)
     }
 
   BDBGPrintf("Adding behavior to class %s\n", class_getName(receiver));
-  BDBGPrintf("  instance methods from %s\n", class_getName(behavior));
 
   /* Add instance methods */
   methods = class_copyMethodList(behavior, &count);
+  BDBGPrintf("  instance methods from %s %u\n", class_getName(behavior), count);
   if (methods == NULL)
     {
-      BDBGPrintf("  none.\n");
+      BDBGPrintf("    none.\n");
     }
   else
     {
@@ -821,11 +837,11 @@ GSObjCAddClassBehavior(Class receiver, Class behavior)
     }
 
   /* Add class methods */
-  BDBGPrintf("  class methods from %s\n", class_getName(behavior));
   methods = class_copyMethodList(object_getClass(behavior), &count);
+  BDBGPrintf("  class methods from %s %u\n", class_getName(behavior), count);
   if (methods == NULL)
     {
-      BDBGPrintf("  none.\n");
+      BDBGPrintf("    none.\n");
     }
   else
     {
@@ -868,21 +884,28 @@ GSObjCAddClassOverride(Class receiver, Class override)
     }
 
   BDBGPrintf("Adding override to class %s\n", class_getName(receiver));
-  BDBGPrintf("  instance methods from %s\n", class_getName(override));
 
   /* Add instance methods */
   methods = class_copyMethodList(override, &count);
-  if (methods != NULL)
+  BDBGPrintf("  instance methods from %s %u\n", class_getName(override), count);
+  if (methods == NULL)
+    {
+      BDBGPrintf("    none.\n");
+    }
+  else
     {
       GSObjCAddMethods (receiver, methods, YES);
       free(methods);
     }
 
   /* Add class methods */
-  BDBGPrintf("Adding class methods from %s\n",
-    class_getName(object_getClass(override)));
   methods = class_copyMethodList(object_getClass(override), &count);
-  if (methods != NULL)
+  BDBGPrintf("  class methods from %s %u\n", class_getName(override), count);
+  if (methods == NULL)
+    {
+      BDBGPrintf("    none.\n");
+    }
+  else
     {
       GSObjCAddMethods (object_getClass(receiver), methods, YES);
       free(methods);
diff --git a/Source/NSObject.m b/Source/NSObject.m
index e5118668a..0f906e471 100644
--- a/Source/NSObject.m
+++ b/Source/NSObject.m
@@ -995,7 +995,6 @@ objc_create_block_classes_as_subclasses_of(Class super) __attribute__((weak));
       fedisableexcept(FE_INVALID);
 #endif
 
-
 #ifdef HAVE_LOCALE_H
       GSSetLocaleC(LC_ALL, "");		// Set up locale from environment.
 #endif
@@ -1003,6 +1002,10 @@ objc_create_block_classes_as_subclasses_of(Class super) __attribute__((weak));
       // Create the global lock
       gnustep_global_lock = [NSRecursiveLock new];
 
+      // Behavior debugging
+      GSObjCBehaviorDebug(GSPrivateEnvironmentFlag("GNUSTEP_BEHAVIOR_DEBUG",
+	GSObjCBehaviorDebug(-1)));
+
       // Zombie management stuff.
       zombieMap = NSCreateMapTable(NSNonOwnedPointerMapKeyCallBacks,
 	NSNonOwnedPointerMapValueCallBacks, 0);