With the expectable growth of the number of Web services available on the WWW and service repositories, the need for mechanisms that enable the automatic organization and discovery of services becomes increasingly important. Service classification using standard or proprietary taxonomies is a common and simple facility in this context, complementarily to more sophisticated service management retrieval techniques. In this paper we propose a heuristic approach for the semi-automatic classification of Web services, based on a three-level matching procedure between services and classification categories, assuming a corpus of previously classified services is available. An experimental test of the proposed techniques is reported, showing positive results.