diff --git a/include/osg/Referenced b/include/osg/Referenced
index ae09f58bf..c04af59e1 100644
--- a/include/osg/Referenced
+++ b/include/osg/Referenced
@@ -59,6 +59,9 @@ class OSG_EXPORT Referenced
         /** Get whether a mutex is used to ensure ref() and unref() are thread safe.*/
         bool getThreadSafeRefUnref() const { return _refMutex!=0; }
 
+        /** Get the mutex used to ensure thread safety of ref()/unref(). */
+        OpenThreads::Mutex* getRefMutex() const { return _refMutex; }
+
         /** Increment the reference count by one, indicating that 
             this object has another pointer which is referencing it.*/
         inline void ref() const;
diff --git a/src/osg/Drawable.cpp b/src/osg/Drawable.cpp
index 761491d5f..15af2fe85 100644
--- a/src/osg/Drawable.cpp
+++ b/src/osg/Drawable.cpp
@@ -313,13 +313,32 @@ void Drawable::computeDataVariance()
 
 void Drawable::addParent(osg::Node* node)
 {
-    _parents.push_back(node);    
+    if (getRefMutex())
+    {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getRefMutex());
+
+        _parents.push_back(node);
+    }
+    else
+    {
+        _parents.push_back(node);
+    }
 }
 
 void Drawable::removeParent(osg::Node* node)
 {
-    ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),node);
-    if (pitr!=_parents.end()) _parents.erase(pitr);
+    if (getRefMutex())
+    {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getRefMutex());
+
+        ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),node);
+        if (pitr!=_parents.end()) _parents.erase(pitr);
+    }
+    else
+    {
+        ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),node);
+        if (pitr!=_parents.end()) _parents.erase(pitr);
+    }
 }
 
 
diff --git a/src/osg/Node.cpp b/src/osg/Node.cpp
index 67e041202..d60571f5d 100644
--- a/src/osg/Node.cpp
+++ b/src/osg/Node.cpp
@@ -95,13 +95,32 @@ Node::~Node()
 
 void Node::addParent(osg::Group* node)
 {
-    _parents.push_back(node);
+    if (getRefMutex())
+    {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getRefMutex());
+
+        _parents.push_back(node);
+    }
+    else
+    {
+        _parents.push_back(node);
+    }
 }
 
 void Node::removeParent(osg::Group* node)
 {
-    ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),node);
-    if (pitr!=_parents.end()) _parents.erase(pitr);
+    if (getRefMutex())
+    {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getRefMutex());
+
+        ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),node);
+        if (pitr!=_parents.end()) _parents.erase(pitr);
+    }
+    else
+    {
+        ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),node);
+        if (pitr!=_parents.end()) _parents.erase(pitr);
+    }
 }
 
 void Node::accept(NodeVisitor& nv)
diff --git a/src/osg/StateSet.cpp b/src/osg/StateSet.cpp
index c7137b8e8..faafedd01 100644
--- a/src/osg/StateSet.cpp
+++ b/src/osg/StateSet.cpp
@@ -78,7 +78,8 @@ bool osg::isTextureMode(StateAttribute::GLMode mode)
     return getTextureGLModeSet().isTextureMode(mode);
 }
 
-StateSet::StateSet()
+StateSet::StateSet():
+    Object(true)
 {
     _renderingHint = DEFAULT_BIN;
     
@@ -247,14 +248,32 @@ void StateSet::computeDataVariance()
 void StateSet::addParent(osg::Object* object)
 {
     // osg::notify(osg::INFO)<<"Adding parent"<<std::endl;
+    if (getRefMutex())
+    {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getRefMutex());
 
-    _parents.push_back(object);
+        _parents.push_back(object);
+    }
+    else
+    {
+        _parents.push_back(object);
+    }
 }
 
 void StateSet::removeParent(osg::Object* object)
 {
-    ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),object);
-    if (pitr!=_parents.end()) _parents.erase(pitr);
+    if (getRefMutex())
+    {
+        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(*getRefMutex());
+
+        ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),object);
+        if (pitr!=_parents.end()) _parents.erase(pitr);
+    }
+    else
+    {
+        ParentList::iterator pitr = std::find(_parents.begin(),_parents.end(),object);
+        if (pitr!=_parents.end()) _parents.erase(pitr);
+    }
 }
 
 int StateSet::compare(const StateSet& rhs,bool compareAttributeContents) const