Prescribing antibiotics for perioperative prophylaxis in common surgical procedures presents an ideal target for educational intervention. In this situation, antibiotics are often used inappropriately, with consequent excess expense and risk of morbidity. We developed an educational intervention aimed at the choice and appropriate dosing of antibiotics for the prophylaxis of cesarean sections. Person-to-person educational messages targeted at authoritative senior department members were supplemented by brief reminders on a structured antibiotic order form. Time-series analyses were conducted on 34 months of antibiotic use data for 2,783 cesarean sections to estimate the trend of magnitude and significance of discontinuities associated with the start of the program. Prior to the intervention, 95% of sections receiving prophylaxis were given cefoxitin and 3% were given cefazolin. After the intervention, these proportions were reversed, with the shift in use occurring immediately after the intervention (p less than .001). Two years after the intervention, virtually all patients undergoing cesarean sections who receive antibiotic prophylaxis are given cefazolin. Savings from this change alone accounted for over $26,000 each year, or $47.36 per patient-day of prophylaxis. Substantial changes in prescribing practices for routine procedures can be accomplished through the implementation of a coordinated educational program that enlists influential senior staff members in a department in which policy-making is highly centralized, coupled with a structured educational ordering system. Lasting improvements in clinical practices may be brought about by means that are noncoercive, inexpensive and well-accepted by medical staff.