Next issue. My callback isn't being hit when I change the value in the master dropdown. I have the code below...simplified, albeit apparently wrong. Unlike the examples, the #ahah being added to the field does not result in any ahah references in jQuery.extend(Drupal.settings. function test_menu() { $items = array(); $items['test/dropdown/callback'] = array( 'page callback' => 'test_do_callback', 'type' => MENU_CALLBACK, 'access_callback' => TRUE, ); return $items; } function test_form_alter(&$form, &$form_state, $form_id) { if ($form_id == 'test_profile_node_form') { $form['field_two']['#prefix'] = '<div id="field-two-wrapper">'; $form['field_two']['#suffix'] = '</div>'; $form['field_master']['#ahah'] = array( 'path' => 'test/dropdown/callback', 'wrapper' => 'field-two-wrapper' ); $form['field_master']['#tree'] = TRUE; } } function test_do_callback() { // do stuff here }