diff --git a/core/src/main/java/hudson/model/AbstractProject.java b/core/src/main/java/hudson/model/AbstractProject.java
index e9c01f8a496a431c6a10eb3abcd7602b497cdb54..cc2b36387d6c63ef2f8b27409cbe8e0af9388e01 100644
--- a/core/src/main/java/hudson/model/AbstractProject.java
+++ b/core/src/main/java/hudson/model/AbstractProject.java
@@ -3,7 +3,8 @@
  * 
  * Copyright (c) 2004-2010, Sun Microsystems, Inc., Kohsuke Kawaguchi,
  * Brian Westrich, Erik Ramfelt, Ertan Deniz, Jean-Baptiste Quenot,
- * Luca Domenico Milanesio, R. Tyler Ballance, Stephen Connolly, Tom Huybrechts, id:cactusman
+ * Luca Domenico Milanesio, R. Tyler Ballance, Stephen Connolly, Tom Huybrechts,
+ * id:cactusman, Yahoo! Inc.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,6 +26,8 @@
  */
 package hudson.model;
 
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 import antlr.ANTLRException;
 import hudson.AbortException;
 import hudson.CopyOnWrite;
@@ -1763,6 +1766,63 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
                 return FormValidation.warning("There's no slave/cloud that matches this assignment");
             return FormValidation.ok();
         }
+
+       public AutoCompletionCandidates doAutoCompleteAssignedLabelString(@QueryParameter String value) {
+            AutoCompletionCandidates c = new AutoCompletionCandidates();
+            Set<Label> labels = Hudson.getInstance().getLabels();
+            List<String> queries = new AutoCompleteSeeder(value).getSeeds();
+
+            for (String term : queries) {
+                for (Label l : labels) {
+                    if (l.getName().startsWith(term)) {
+                        c.add(l.getName());
+                    }
+                }
+            }
+            return c;
+        }
+
+        /**
+        * Utility class for taking the current input value and computing a list
+        * of potential terms to match against the list of defined labels.
+         */
+        static class AutoCompleteSeeder {
+            private String source;
+            private Pattern quoteMatcher = Pattern.compile("(\\\"?)(.+?)(\\\"?+)(\\s*)");
+
+            AutoCompleteSeeder(String source) {
+                this.source = source;
+            }
+
+            List<String> getSeeds() {
+                ArrayList<String> terms = new ArrayList();
+                boolean trailingQuote = source.endsWith("\"");
+                boolean leadingQuote = source.startsWith("\"");
+                boolean trailingSpace = source.endsWith(" ");
+
+                if (trailingQuote || (trailingSpace && !leadingQuote)) {
+                    terms.add("");
+                } else {
+                    if (leadingQuote) {
+                        int quote = source.lastIndexOf('"');
+                        if (quote == 0) {
+                            terms.add(source.substring(1));
+                        } else {
+                            terms.add("");
+                        }
+                    } else {
+                        int space = source.lastIndexOf(' ');
+                        if (space > -1) {
+                            terms.add(source.substring(space+1));
+                        } else {
+                            terms.add(source);
+                        }
+                    }
+                }
+
+                return terms;
+            }
+        }
     }
 
     /**
diff --git a/core/src/main/resources/hudson/model/AbstractItem/configure-common.jelly b/core/src/main/resources/hudson/model/AbstractItem/configure-common.jelly
index 7d5c2ae4cbf2450c424c47108b28351a324b43ca..fb40c916659dda8b8133f7e2af8c36262e8baffe 100644
--- a/core/src/main/resources/hudson/model/AbstractItem/configure-common.jelly
+++ b/core/src/main/resources/hudson/model/AbstractItem/configure-common.jelly
@@ -1,7 +1,8 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Eric Lefevre-Ardant, id:cactusman
+Copyright (c) 2004-2010, Sun Microsystems, Inc., Kohsuke Kawaguchi,
+Eric Lefevre-Ardant, id:cactusman, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -50,7 +51,7 @@ THE SOFTWARE.
     <f:optionalBlock name="hasSlaveAffinity" title="${%Restrict where this project can be run}" checked="${it.assignedLabel!=null}"
         help="/help/project-config/slave.html">
       <f:entry title="${%Label Expression}" field="assignedLabelString">
-        <f:textbox />
+        <f:textbox autoCompleteDelimiChar=" "/>
       </f:entry>
     </f:optionalBlock>
   </j:if>
diff --git a/core/src/main/resources/lib/form/textbox.jelly b/core/src/main/resources/lib/form/textbox.jelly
index 1461bd1f1331cce6636adc804fea3f0b27239949..040e5e74c376e35f558ca2221d4fc41c1a0164b8 100644
--- a/core/src/main/resources/lib/form/textbox.jelly
+++ b/core/src/main/resources/lib/form/textbox.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+Copyright (c) 2004-2010, Sun Microsystems, Inc., Kohsuke Kawaguchi, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -59,6 +59,12 @@ THE SOFTWARE.
       If @field is specified, this will be inferred automatically,
       which is the recommended approach.
     </st:attribute>
+    <st:attribute name="autoCompleteDelimChar">
+      A single character that can be used as a delimiter for autocompletion. Normal
+      autocomplete will replace the entire content of the text box with the autocomplete
+      selection. With this attribute set, the selection will be appended with the
+      delimiter to the existing value of the text box.
+    </st:attribute>
   </st:documentation>
   <f:prepareDatabinding />
   ${descriptor.calcAutoCompleteSettings(field,attrs)} <!-- this figures out the 'autoCompleteUrl' attribute -->
diff --git a/core/src/test/java/hudson/model/AutoCompleteSeederTest.java b/core/src/test/java/hudson/model/AutoCompleteSeederTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..256938165a9c07b025a03844339856d16f814b44
--- /dev/null
+++ b/core/src/test/java/hudson/model/AutoCompleteSeederTest.java
@@ -0,0 +1,86 @@
+/*
+ *  The MIT License
+ * 
+ *  Copyright 2010 Yahoo! Inc.
+ * 
+ *  Permission is hereby granted, free of charge, to any person obtaining a copy
+ *  of this software and associated documentation files (the "Software"), to deal
+ *  in the Software without restriction, including without limitation the rights
+ *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *  copies of the Software, and to permit persons to whom the Software is
+ *  furnished to do so, subject to the following conditions:
+ * 
+ *  The above copyright notice and this permission notice shall be included in
+ *  all copies or substantial portions of the Software.
+ * 
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ *  THE SOFTWARE.
+ */
+
+package hudson.model;
+
+import java.util.List;
+import java.util.Arrays;
+import java.util.Collection;
+import org.junit.runners.Parameterized;
+import org.junit.runner.RunWith;
+import hudson.model.AbstractProject.AbstractProjectDescriptor.AutoCompleteSeeder;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+/**
+ *
+ * @author dty
+ */
+@RunWith(Parameterized.class)
+public class AutoCompleteSeederTest {
+
+    public static class TestData {
+        private String seed;
+        private List<String> expected;
+        
+        public TestData(String seed, String... expected) {
+            this.seed = seed;
+            this.expected = Arrays.asList(expected);
+        }
+    }
+    
+    @Parameterized.Parameters
+    public static Collection<Object[]> data() {
+        return Arrays.asList( new Object[][] {
+                    { new TestData("", "") },
+                    { new TestData("\"", "") },
+                    { new TestData("\"\"", "") },
+                    { new TestData("freebsd", "freebsd") },
+                    { new TestData(" freebsd", "freebsd") },
+                    { new TestData("freebsd ", "") },
+                    { new TestData("freebsd 6", "6") },
+                    { new TestData("\"freebsd", "freebsd") },
+                    { new TestData("\"freebsd ", "freebsd ") },
+                    { new TestData("\"freebsd\"", "") },
+                    { new TestData("\"freebsd\" ", "") },
+                    { new TestData("\"freebsd 6", "freebsd 6") },
+                    { new TestData("\"freebsd 6\"", "") },
+               });
+    }
+
+    private String seed;
+    private List<String> expected;
+
+    public AutoCompleteSeederTest(TestData dataSet) {
+        this.seed = dataSet.seed;
+        this.expected = dataSet.expected;
+    }
+
+    @Test
+    public void testAutoCompleteSeeds() throws Exception {
+        AutoCompleteSeeder seeder = new AbstractProject.AbstractProjectDescriptor.AutoCompleteSeeder(seed);
+        assertEquals(expected, seeder.getSeeds());
+
+    }
+}
\ No newline at end of file
diff --git a/war/src/main/webapp/scripts/hudson-behavior.js b/war/src/main/webapp/scripts/hudson-behavior.js
index 097ea3a0a096804583a13cf865cee2a81a2b67c5..0647d5f1efd001f15d3888b455b3a54dd239ee58 100644
--- a/war/src/main/webapp/scripts/hudson-behavior.js
+++ b/war/src/main/webapp/scripts/hudson-behavior.js
@@ -605,6 +605,7 @@ var hudsonRules = {
         ac.animSpeed = 0;
         ac.useShadow = true;
         ac.autoSnapContainer = true;
+        ac.delimChar = e.getAttribute("autoCompleteDelimiChar");
         ac.doBeforeExpandContainer = function(textbox,container) {// adjust the width every time we show it
             container.style.width=textbox.clientWidth+"px";
             var Dom = YAHOO.util.Dom;