The MENTOR system is designed to address the problem of adverse drug reactions in hospitalized patients by monitoring their drug therapy. It combines the automated collection of data with the complex reasoning processes of expert systems into a computer system for continuously monitoring therapeutic interventions for hospitalized patients. It implements a patient monitoring cycle that follows and evaluates the treatment of individual patients and provides appropriate advisory messages to physicians and other health care professionals. At any point in time, the set of events of interest to the MENTOR system for a specific patient is determined by his or her current drug therapy, surgical procedures and laboratory tests. The MENTOR system builds a dynamic profile of these events for each patient that determines what types of monitoring will be done as well as when and what types of evaluation will be carried out each time an event is detected. The system's knowledge base currently deals with aminoglycosides, surgical prophylaxis, digoxin, and blood culture results.