The usage of semantic web services in enterprise computing promises many advantages. Instead of hard-wiring web services in business processes during design-time, business experts just specify the expected functionality and matching semantic web services are bound automatically during runtime. However, the introduction of semantic web services requires the replacement or extension of existing middleware and standards. We suggest a more realistic approach based on existing standards like BPEL. Therefore we introduce the Semantic Invocation Service (SISi), which handles semantic web service calls.