--- src/core/org/apache/jmeter/threads/JMeterContext.java	(revision 1166194)
+++ src/core/org/apache/jmeter/threads/JMeterContext.java	(working copy)
@@ -65,6 +65,7 @@ 
         samplingStarted = false;
         threadNum = 0;
         readBuffer = null;
+        thread = null;
     }
 
     /**
--- src/core/org/apache/jmeter/threads/JMeterThread.java	(revision 1166194)
+++ src/core/org/apache/jmeter/threads/JMeterThread.java	(working copy)
@@ -20,9 +20,12 @@ 
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.ListIterator;
+import java.util.Map;
+import java.util.Set;
 
 import org.apache.jmeter.assertions.Assertion;
 import org.apache.jmeter.assertions.AssertionResult;
@@ -123,6 +126,11 @@ 
 
     private volatile Sampler currentSampler;
 
+    /**
+     * Variables backup state at start of run 
+     */
+    private JMeterVariables threadVarsBkp;
+
     public JMeterThread(HashTree test, JMeterThreadMonitor monitor, ListenerNotifier note) {
         this.monitor = monitor;
         threadVars = new JMeterVariables();
@@ -302,6 +310,28 @@ 
             threadFinished();
             monitor.threadFinished(this); // Tell the engine we are done
             JMeterContextService.removeContext(); // Remove the ThreadLocal entry
+            clearThreadVars();
+        }
+    }
+
+    /**
+     * Clean all variables that have been added by samplers by coming back to initial set
+     */
+    private void clearThreadVars() {
+        Set<String> keysToKeepSet = new HashSet<String>();
+        for (Iterator<Map.Entry<String,Object>> iterator = threadVarsBkp.getIterator(); iterator.hasNext();) {
+            keysToKeepSet.add(iterator.next().getKey());
+        }
+        Set<String> keysToRemoveSet = new HashSet<String>();
+        for (Iterator<Map.Entry<String,Object>> iterator = threadVars.getIterator(); iterator.hasNext();) {
+            Map.Entry<String,Object> entry = iterator.next();
+            if(!keysToKeepSet.contains(entry.getKey()))
+            {
+                keysToRemoveSet.add(entry.getKey());
+            }      
+        }
+        for (String key : keysToRemoveSet) {
+            threadVars.remove(key);
         }
     }
 
@@ -473,6 +503,8 @@ 
      *
      */
     private void initRun(JMeterContext threadContext) {
+        threadVarsBkp = new JMeterVariables();
+        threadVarsBkp.putAll(threadVars);
         threadContext.setVariables(threadVars);
         threadContext.setThreadNum(getThreadNum());
         threadContext.getVariables().put(LAST_SAMPLE_OK, TRUE);