Within the European HARP project, a Java™-based Open Platform has been specified and implemented to support trustworthy distributed applications for health. Emphasis was put on security services for enabling both communication and application security. The Open Platform is Web-based and comprises the Client environment, Web/Application server, as well as Database and Archive servers. Servlets composed and executed according to the user’s authorisation create signed XML messages. From those messages, user-role-related applets are generated. The technical details of the realisation are presented. Possible future enhancements for user-centric, adaptable services based on next-generation mobile service environments are outlined.