A mechanism lets a service consumer add mediation metadata in a Simple Object Access Protocol (SOAP) message and lets a service provider perform server side mediation based on the pre-defined mediation metadata. A client side mediation engine is plugged into a client SOAP engine. When the client side mediation engine receives a request message from the client SOAP engine metadata is attached to a message header of a SOAP message and returned to the client SOAP engine. A server side mediation engine is plugged the server side mediation engine receives a SOAP message from the server SOAP engine, metadata is mapped with an appropriate adaptor and returned to the server SOAP engine.