This article describes the knowledge-based system TheMPO (Therapy Management in Pediatric Oncology), which supports protocol-directed therapy planning and con guration in pediatric oncology. TheMPO provides a semantic network controlled by graph-grammars to cover the di erent types of knowledge relevant in the domain, and o ers a suite of acquisition tools for knowledge base authoring. Medical problem solvers, operating on the oncological network, reason about adequate therapeutic and diagnostic time-tables for a patient. Furthermore, a corresponding patient record, also based on semantic networks and graph-grammars, has been implemented to represent the course of therapy of an oncological patient.