In studies on success and failure of ICT applications in health care, the 'context' is often used to explain the failure of a system and seldom to explain the success of a system. Science and Technology Studies (STS) have showed that for understanding success and failure of phenomena, one has to take a symmetrical approach and thus use the same concept for analyzing success and failure. In this article we analyze the success of OZIS, a communication protocol that makes it possible for pharmacists to exchange medication data by sharing a regionally accessible electronic medication record. Though OZIS serves a common goal - reducing medication errors - the stakeholders that are involved also have other, competing, interests. By focussing on the context and more specifically the interests of the stakeholders, we will show how the success of OZIS can be explained. By doing this, we will also show that this context is highly dynamic and that continuously changing incentives and constraints within the context lead to both facilitating and threatening the success of OZIS.