This paper presents a middleware to help designers in the implementation of contract-aware agent-based services. The middleware provides several components, including a contract manager, a communication manager and a workflow manager, which combine to allow agents to manage contracts and the actions associated with them. The middleware is built as part of a Web service implementation of the IST-CONTRACT framework. An electronic commerce example is used to illustrate how the components of the middleware facilitates the management and execution of agreements in a contract at run-time.