In this paper we present an approach for reusing agent-based reasoning capabilities by making them available for invocation as Web services. In this way, we provide the missing link between the highly interoperable Web services and the autonomicity and intelligence of agent-based systems, so that the latter can be seamlessly integrated into the knowledge-rich SemanticWeb environment without being compromised by isolated communication platforms and languages or restricted to only one or just few reasoning formalisms. We have achieved this by extending the EMERALD framework for agent based reasoning with a Web service interface. Our approach is exemplified by the development of an online system for intelligent brokering of apartment rentals. The broker intelligence is captured as a defeasible knowledge base, while its problem solving process involves the invocation of third party defeasible reasoning Web services included into the EMERALD framework.