Service Oriented Architectures and Web Services are emerging technologies, which have overall inherited problems and advantages from the component-based approach, but exacerbated the aspects of loose coupling, distribution and dynamism of "components", here elements furnishing published services on external client requests. In this paper we highlight the urgent need for methodologies supporting Web Services reliable interaction, and in particular deal with testing concerns. We then propose a framework that extends UDDI registry role from the current one of a "passive" service directory, to also sort of an accredited testing organism, which validates service behaviour before actually registering it. This testing stage (called audition) mainly focuses on interoperability issues, so to facilitate the coordination among services registered at the same UDDI. The audition needs to rely on a Web Service specification augmented with information on how the service has to be invoked. We propose that this information is given in the form of a Protocol State Machine, which is a newly introduced behaviour diagram of the UML 2.0.