A pharmacy-based antimicrobial-monitoring service at a university teaching hospital is described. The service was developed and implemented by the pharmacy department in 1987. Antimicrobial drugs that can be misused, that are expensive, or for which bacterial resistance is a concern were targeted. When a pharmacist receives an order for a targeted antimicrobial, an antimicrobial-monitoring card is completed. Monitored drugs meeting approved criteria are dispensed as ordered. When the antimicrobial does not meet the criteria, the pharmacist contacts the physician and suggests an alternative. If the alternative is not accepted, the infectious diseases service is contacted and then informs the pharmacy department about the status of the drug. The agent is dispensed if no response is received within two hours. Qualified staff pharmacists rotate through the position of antimicrobial pharmacist, whose responsibilities include reviewing antimicrobial use throughout the hospital, checking relevant laboratory test results, and recommending adjustments to regimens. From July 1989 to June 1990, 3546 orders for monitored antimicrobials were reviewed; of these, 86% met the criteria, 9% did not meet the criteria but were approved, 2% were for drugs that were replaced by alternative therapies, 1% were for agents that were dispensed because the pharmacist was not contacted, and 2% represented medical staff overrides or drugs dispensed inappropriately. Pharmacist and physician compliance with the monitoring policy has been high. A positive, constructive, and educational relationship exists between pharmacists and physicians vis-à-vis the service. A pharmacy-based antimicrobial-monitoring service has been accepted by pharmacists and physicians and appears to be having a positive impact on prescribing habits.