Some items come in a variety of media formats. For example, a book might come in hardback, paperback, audio cassette, audio CD, and DVD. A person buying an item in one format might be interested in the same item presented in a different format. To return all of the media formats of a single item, Product Advertising API provides the AlternateVersions response group. The catch is, the response group only works with items in the Books or ForeignBooks product categories. That means, for ItemSearch and ItemLookup, the search index must be Books or, in non-US locales, ForeignBooks, and, for ItemLookup, the specified item must be a book or foreign book.

http://ecs.amazonaws.com/onca/xml?
Service=AWSECommerceService&
Operation=ItemSearch&
AWSAccessKeyId=[AWS Access Key ID]&
AssociateTag=ws&
SearchIndex=Books&
Keywords=potter&
MerchantId=All&
ResponseGroup=AlternateVersions&
Version=2006-06-28

This request returns books and media in other formats that contain "potter" in their title or product description, as shown in the following snippet of the response.

<AlternateVersions>
  <AlternateVersion>
    <ASIN>030728364X</ASIN>
    <Title>Harry Potter and the Half-Blood Prince (Book 6)
    </Title>
    <Binding>Audio Cassette</Binding>
  </AlternateVersion>
  <AlternateVersion>
    <ASIN>0307283658</ASIN>
    <Title>Harry Potter and the Half-Blood Prince (Book 6)
    </Title>
    <Binding>Audio CD</Binding>
  </AlternateVersion>
</AlternateVersions>

This response shows that the book, Harry Potter and the Half-Blood Prince, is available on audio cassette and CD.