Prophylactic antibiotics were given postoperatively to a consecutive series of 74 patients who underwent vaginal hysterectomy. Antibiotics were administered in the immediate postoperative period. There was a highly significant decrease in febrile morbidity in the treated group compared to 190 control subjects having similar surgery but treated with antibiotics only on the appearance of fever and/or other signs of infection. There was a failure to relate the increased febrile morbidity in the control group to patient's age, menopausal state, type of catheterization, or to the type of operative procedure. The increased morbidity in the control group related only to the failure to use prophylactic antibiotics. The antibiotic-treated portion (58 per cent) of the control group had a longer period of hospitalization.