This paper introduces ubiquitous healthcare, addressing the access of health services by individual consumers applying to mobile computing devices. This access requires knowledge about the individual health status, which may involve (as far as available) the current personal situation (e.g., accident), relevant recent diseases etc., current symptoms or already available diagnosis. Addressing the related IT challenges - e.g., patient-centric knowledge processing, situation awareness, local control - we develop in detail the OnkoNet Mobile Agents Architecture involving architectures on the macrolevel and microlevel as well as cooperation protocols, inference models controlling system behaviour, and a health ontology.