A computer-assisted, pharmacy-managed antimicrobial surveillance service is described. Rising drug costs and inappropriate use of antimicrobial drugs led to the January 1994 implementation of an antimicrobial surveillance program at a 369-bed community teaching hospital. A computer interface between the pharmacy and microbiology laboratory data-bases was established that allows pharmacists quick access to culture and susceptibility test results and provides timely reports identifying patients for whom intervention may be necessary. Pharmacists review the reports, assess the patient's condition, and, when appropriate, recommend changes in therapy to the prescribing physician. Data on interventions, costs, and outcomes are reviewed monthly. From January to July 1994, pharmacists monitored the antimicrobial therapy of 1384 patients. Interventions were recommended for 348 patients (25%). Physicians accepted 289 (83%) of the recommendations. The infection subsided in 280 (97%) of the patients for whom recommendations were accepted. The cost avoidance achieved by the interventions exceeded $32,000, which more than justified the one full-time pharmacist position assigned to the service. A computer-assisted antimicrobial surveillance service managed by pharmacists helped control costs and achieve favorable clinical outcomes.