diff --git drush.php drush.php
index 014ae72..9fb58d1 100755
--- drush.php
+++ drush.php
@@ -92,6 +92,7 @@ function drush_main() {
         drush_enforce_requirement_bootstrap_phase($command);
         drush_enforce_requirement_core($command);
         drush_enforce_requirement_drupal_dependencies($command);
+        drush_enforce_requirement_drush_dependencies($command);
 
         if ($bootstrap_result && empty($command['bootstrap_errors'])) {
           drush_log(dt("Found command: !command (commandfile=!commandfile)", array('!command' => $command['command'], '!commandfile' => $command['commandfile'])), 'bootstrap');
diff --git includes/command.inc includes/command.inc
index 978a2b8..c6f7c28 100644
--- includes/command.inc
+++ includes/command.inc
@@ -628,7 +628,7 @@ function drush_command_defaults($key, $commandfile, $path) {
  * - bootstrap: drupal bootstrap level (depends on Drupal major version). -1=no_bootstrap.
  * - core: Drupal major version required.
  * - drupal dependencies: drupal modules required for this command.
- * - drush dependencies: other drush command files required for this command (not yet implemented)
+ * - drush dependencies: other drush command files required for this command
  *
  * @example
  *   drush_parse_command();
@@ -1153,6 +1153,33 @@ function drush_enforce_requirement_drupal_dependencies(&$command) {
 }
 
 /**
+ * Check that a command has its declared drush dependencies available or have no
+ * dependencies.
+ *
+ * @param $command
+ *   Command to check. Any errors  will be added to the 'bootstrap_errors' element.
+ * @return
+ *   TRUE if dependencies are met.
+ */
+function drush_enforce_requirement_drush_dependencies(&$command) {
+  // If there are no drupal dependencies, then do nothing
+  if (!empty($command['drush dependencies'])) {
+    $commandfiles = drush_commandfile_list();
+    foreach ($command['drush dependencies'] as $dependency) {
+      if (!isset($commandfiles[$dependency])) {
+        $dt_args = array(
+          '!command' => $command['command'],
+          '!dependency' => "$dependency.drush.inc",
+        );
+        $command['bootstrap_errors']['DRUSH_COMMAND_DEPENDENCY_ERROR'] = dt('Command !command needs the following drush command file to run: !dependency.', $dt_args);
+        return FALSE;
+      }
+    }
+  }
+  return TRUE;
+}
+
+/**
  * Check that a command is valid for the current major version of core.
  *
  * @param $command