We studied the clinical and microbiological response to two treatment regimens in 36 patients with acute pelvic inflammatory disease (PID). All patients were hospitalized and underwent laparoscopy and endometrial biopsy. Cervical, endometrial, tubal and peritoneal cultures for Chlamydia trachomatis, Neisseria gonorrhoeae, genital mycoplasmas, facultative and anaerobic bacteria and Herpes simplex virus were obtained. The patients were randomly assigned to two treatment groups: 16 women received ciprofloxacin 200 mg b.i.d. iv. for two days, followed by oral administration with 750 mg b.i.d. to complete a 14-day course of treatment. Twenty women received the combination of doxycycline and metronidazole according to a similar scheme of administration. The response was evaluated with repeated clinical examinations, monitoring of the erythrocyte sedimentation rate and serum C-reactive protein concentration, and repeated microbial culture from the cervix. Ciprofloxacin treatment was successful in all nine patients with chlamydial or gonococcal PID and in six of seven with nonchlamydial nongonococcal PID. Doxycycline plus metronidazole regimen was successful in five of seven patients with chlamydial or gonococcal PID and in nine of 13 patients with nonchlamydial nongonococcal PID. Thus, the overall success rate was 94% (15 of 16) with ciprofloxacin and 70% (14 of 20) with doxycycline plus metronidazole. Our study suggests that ciprofloxacin is a promising new alternative for the treatment of acute PID.