The Computer Systems Laboratory and the Pharmacy Department of the Clinical Center are in collaboration to develop an expert system for the generation and analysis of patient medication histories. This analysis is a complete and comprehensive report of the patient medication status that is given to the physician for review before the patient examination. The project originated from a need for pharmacist initiated patient medication histories. The system is being developed on an IBM/AT computer using a CSL designed forward chaining inference mechanism, and the MEDICOM (c) Drug Interaction Database, produced by Professional Drug Systems. The system has three databases: the knowledge base, the drug database, and the patient data. The knowledge base contains the expert clinical knowledge of the pharmacist, for a specific clinical domain, and works in conjunction with the Drug Interaction Database to evaluate the patient data, as gathered through questionnaires. The analysis includes a comprehensive medication history, warning of possible medication toxicity, and warning of potential medication interactions. A comprehensive medication history includes the current medications, past medications, and all over-the-counter and/or prescription medications for other common problems.