Index: ports/classes/net/xp_framework/unittest/reflection/FieldsTest.class.php
===================================================================
--- ports/classes/net/xp_framework/unittest/reflection/FieldsTest.class.php	(revision 12376)
+++ ports/classes/net/xp_framework/unittest/reflection/FieldsTest.class.php	(working copy)
@@ -178,16 +178,41 @@
     }
 
     /**
+     * Tests reading and writing the "date" field
+     *
+     * @see     xp://lang.reflect.Field#get
+     * @see     xp://lang.reflect.Field#set
+     */
+    #[@test]
+    public function dateFieldRoundTrip() {
+      $instance= $this->fixture->newInstance();
+      $date= Date::now();
+      $field= $this->fixture->getField('date');
+      $field->set($instance, $date);
+      $this->assertEquals($date, $field->get($instance));
+    }
+
+    /**
      * Tests retrieving the "date" field's value on a wrong object
      *
      * @see     xp://lang.reflect.Field#get
      */
     #[@test, @expect('lang.IllegalArgumentException')]
-    public function dateFieldValueOnWrongObject() {
+    public function getDateFieldValueOnWrongObject() {
       $this->fixture->getField('date')->get(new Object());
     }
 
     /**
+     * Tests writing the "date" field's value on a wrong object
+     *
+     * @see     xp://lang.reflect.Field#set
+     */
+    #[@test, @expect('lang.IllegalArgumentException')]
+    public function setDateFieldValueOnWrongObject() {
+      $this->fixture->getField('date')->set(new Object(), Date::now());
+    }
+
+    /**
      * Tests retrieving the "initializerCalled" field's value
      *
      * @see     xp://lang.reflect.Field#get
@@ -198,26 +223,62 @@
     }
 
     /**
+     * Tests retrieving the "initializerCalled" field's value
+     *
+     * @see     xp://lang.reflect.Field#get
+     * @see     xp://lang.reflect.Field#set
+     */
+    #[@test]
+    public function initializerCalledFieldRoundTrip() {
+      with ($f= $this->fixture->getField('initializerCalled')); {
+        $f->set(NULL, FALSE);
+        $this->assertEquals(FALSE, $f->get(NULL));
+        $f->set(NULL, TRUE);
+        $this->assertEquals(TRUE, $f->get(NULL));
+      }
+    }
+
+    /**
      * Tests retrieving the private static "cache" field's value
      *
      * @see     xp://lang.reflect.Field#get
      */
     #[@test, @expect('lang.IllegalAccessException')]
-    public function cacheFieldValue() {
+    public function getCacheFieldValue() {
       $this->fixture->getField('cache')->get(NULL);
     }
 
     /**
+     * Tests setting the private static "cache" field's value
+     *
+     * @see     xp://lang.reflect.Field#set
+     */
+    #[@test, @expect('lang.IllegalAccessException')]
+    public function setCacheFieldValue() {
+      $this->fixture->getField('cache')->set(NULL, array());
+    }
+
+    /**
      * Tests retrieving the protected "size" field's value
      *
      * @see     xp://lang.reflect.Field#get
      */
     #[@test, @expect('lang.IllegalAccessException')]
-    public function sizeFieldValue() {
+    public function getSizeFieldValue() {
       $this->fixture->getField('size')->get($this->fixture->newInstance());
     }
 
     /**
+     * Tests setting the protected "size" field's value
+     *
+     * @see     xp://lang.reflect.Field#set
+     */
+    #[@test, @expect('lang.IllegalAccessException')]
+    public function setSizeFieldValue() {
+      $this->fixture->getField('size')->set($this->fixture->newInstance(), 1);
+    }
+
+    /**
      * Tests retrieving the private "factor" field's value
      *
      * @see     xp://lang.reflect.Field#get
Index: skeleton/lang/reflect/Field.class.php
===================================================================
--- skeleton/lang/reflect/Field.class.php	(revision 12387)
+++ skeleton/lang/reflect/Field.class.php	(working copy)
@@ -96,6 +96,41 @@
     }
 
     /**
+     * Changes the value of the field represented by this Field, on the 
+     * specified object.
+     *
+     * @param   lang.Object instance
+     * @param   mixed value
+     * @throws  lang.IllegalArgumentException in case the passed object is not an instance of the declaring class
+     * @throws  lang.IllegalAccessException in case this field is not public
+     */
+    public function set($instance, $value) {
+    
+      // Verify the field is public
+      if (!($this->_reflect->getModifiers() & MODIFIER_PUBLIC)) {
+        throw new IllegalAccessException('Cannot write '.$this->toString());
+      }
+
+      // Short-circuit further checks for static members
+      if ($this->_reflect->isStatic()) {
+        return $this->_reflect->setValue(NULL, $value);
+      }
+
+      // Verify given instance is instance of the class declaring this 
+      // property
+      if (!($instance instanceof $this->_class)) {
+        throw new IllegalArgumentException(sprintf(
+          'Passed argument is not a %s class (%s)',
+          xp::nameOf($this->_class),
+          xp::typeOf($instance)
+        ));
+      }
+
+
+      $this->_reflect->setValue($instance, $value);
+    }
+
+    /**
      * Retrieve this field's modifiers
      *
      * @see     xp://lang.reflect.Modifiers
Index: skeleton/remote/protocol/Serializer.class.php
===================================================================
--- skeleton/remote/protocol/Serializer.class.php	(revision 12376)
+++ skeleton/remote/protocol/Serializer.class.php	(working copy)
@@ -313,7 +313,7 @@
           $serialized->offset++;  // Opening "{"
           for ($i= 0; $i < $size; $i++) {
             $member= $this->valueOf($serialized, $context);
-            $instance->{$member}= $this->valueOf($serialized, $context);
+            $class->getField($member)->set($instance, $this->valueOf($serialized, $context));
           }
           $serialized->offset++; // Closing "}"
           return $instance;