diff --git a/src/Amazon.php b/src/Amazon.php
index ecfe5c5..0c65c67 100644
--- a/src/Amazon.php
+++ b/src/Amazon.php
@@ -121,12 +121,14 @@ class Amazon {
    *
    * @param array|string $items
    *   A string containing a single ASIN, or an array of ASINs, to look up.
+   * @param array $response_groups
+   *   (optional) List of additional response groups to be returned.
    *
    * @return array
    *   An array of SimpleXMLElement objects representing the response from
    *   Amazon.
    */
-  public function lookup($items) {
+  public function lookup($items, $response_groups = []) {
     if (empty($items)) {
       throw new \InvalidArgumentException('Calling lookup without anything to lookup!');
     }
@@ -135,11 +137,12 @@ class Amazon {
     }
 
     $results = [];
+    $response_groups = array_merge(['Small', 'Images'], $response_groups);
     // Cannot ask for info from more than 10 items in a single call.
     foreach(array_chunk($items, 10) as $asins) {
       $lookup = new Lookup();
       $lookup->setItemIds($asins);
-      $lookup->setResponseGroup(['Small', 'Images']);
+      $lookup->setResponseGroup($response_groups);
       $results = array_merge($results, $this->apaiIO->runOperation($lookup));
     }
     return $results;