Thirty-eight patients presenting with septic abortion were treated with intravenous cephalothin, 8 g/day. Eighteen patients treated with other antibiotics served as controls. Based on temperature response and decrease in leukocytosis, cephalothin proved efficacious, but its action was slower than that of the other antibiotics used (in most cases penicillin combined with a broad-spectrum antibiotic). This suggests that penicillin in combination with a broad-spectrum antibiotic is the preferable therapy for patients with septic abortions; cephalothin may be the antibiotic of choice when penicillin allergy is suspected.