The SENEX project has been initiated at the fondation Bergonié in 1985 and is intended for providing physicians in general hospitals with knowledge based systems for the management of cancer treatment protocols. The design and building of a knowledge-based system for the management of breast cancer protocols (SENEX) was the first goal of this project. SENEX has been developed using a commercially available development tool (Personal Consultant Plus, Texas-instruments) derived from EMYCIN. It runs on IBM and compatible microcomputers. The knowledge base embeds the formal knowledge contained in the breast cancer protocols currently in use at the fondation Bergonié, and some judgmental knowledge acquired form breast cancer experts. Production rules and frames allowed us to adequately represent and structure this knowledge and the problem solving processes related to the management of breast cancer. A preliminary informal evaluation of the system has shown that it performs at the expert-level in giving advice for patients included in formal protocols. Its use and acceptability are good. However, we have to add judgmental knowledge into the knowledge base and to interface the system with a temporal data base management system to improve the overall performances of SENEX. Moreover the effectiveness of the system remains to be demonstrated before one can anticipate is routine use in clinical practice.