The problem it is not know what type the Object1 and Object2 are, so they are not described in the WSDL. If you really want to return an IList, you can use the System.Xml.Serialization.XmlIncludeAttribute to explicitly add the type of Object1 and Object2 to the WSDL. But like Bart said, I would suggest using a strongly typed collection (inheriting from CollectionBase) or an array. Jan