Because the efficacy of prophylactic antibiotic therapy has yet to be established and because numerous variables often hamper studies of such therapy, the results of prophylactic antibiotic therapy were studied in a homogeneous gynecologic population. The patients were 4000 women undergoing first trimester abortions. The surgical procedure, the gynecologists' skill, and the hospital environment were relatively uniform, as was the patient age range. Two groups of 1000 patients each received tetracycline; the other 2000 patients served as controls. The complications associated with abortion were then analyzed in those receiving tetracycline and in the 2000 controls. Complications were less frequent among patients receiving tetracycline. This finding supports the argument of those who favor the prophylactic use of antibiotics in the management of various high-risk surgical problems.