Medical treatment of a patient could be represented as a circle of the following actions: examination, diagnostics, and therapy. The aims of the actions are to find out the patient's state of health and consequently to conclude about possible diseases and finally to choose a suitable therapy. In long term, the circle of actions repeat as long as the patient is not healthy. Efficiency of this treatment depends on the knowledge and the experiences of the physicians involved. Information technology offers many possibilities to help the physicians increase the efficiency and the quality of this work. In the article, we present an agent-oriented computer-based health care service, which uses information from different data sources that are physically distributed across several sites. Such a decentralized approach mirrors the organizational structure of a health service and it is very similar to an agent-oriented view of the world.