A prospective, randomized study comparing single dose intravenous antibiotic prophylaxis with multiple-dose regimen in patients undergoing radical surgery for gynecologic malignancy was carried out. The majority of patients had cervical cancer. Thirty-seven patients in group A received one dose of 4 g piperacillin and 800 mg tinidazole 30 minutes before surgery. Twenty-nine patients in group B additionally received 4g piperacillin 8 hours and 4g piperacillin and 800 mg tinidazole 16 hours after the first dose. There were no significant differences between groups A and B with regard to median patient age, performance status, cardiologic and pulmonary status, or frequency of diabetes. There were also no significant differences between either group with regard to the parameters documented postoperatively, such as median hospital stay, leukocyte values, or febrile episodes. Forty-three per cent of patients in group A and 48% of patients in group B had no complications (p > 0.05). Twenty-three per cent of patients in group A and 31% of patients in group B developed infections (p > 0.05), 85% of which occurred in the urinary tract. The data suggest that a single dose of intravenous antibiotics is as effective as multiple dose administration in the perioperative prophylaxis in radical gynecologic surgery.