The development and use of a hospital-pharmacy-based, computer-assisted antimicrobial monitoring program are described. In the pharmacy department of a teaching hospital in Spain, a manual system for collecting data on use of antimicrobial agents was replaced with a computer-assisted program that compiles data on culture and sensitivity results, the number of patients receiving antimicrobial or bacteriostatic agents (including combination therapy), and the specific agents used by hospital ward, clinical department, and physician. The antimicrobial report is reviewed daily by a pharmacist, and identified problems are discussed with the prescribing physician; about two hours per day is spent in this activity. Data for 1984 compiled by the computer program regarding the use of antimicrobial agents by group and by hospital ward and the relationship between cost and use of antimicrobial agents were evaluated. Based on the computer-generated data, guidelines for antibiotic use in surgical prophylaxis were proposed, and the pharmacy and therapeutics committee approved a new antibiotic policy that led to a reduction in the use of cephalosporins and to subsequent cost savings. Antimicrobial use at this hospital is similar to that reported at other institutions. In 1984 penicillins were the most commonly used agents, followed by aminoglycosides and cephalosporins. Antimicrobial agents accounted for 24.4% of all drug costs. This computer-assisted system of antimicrobial monitoring was used effectively to assess both individual patient therapy and overall antimicrobial use in a teaching hospital.