Therapy for acute polymicrobial pelvic infections is empiric and must include predictable anaerobic coverage. Single agent therapy, if effective, is advantageous for the patient, nurses, pharmacy and hospital. Piperacillin sodium was compared with a combination of clindamycin and gentamicin as therapy for 63 female patients who were hospitalized with acute pelvic infections including pelvic abscess complicating community acquired salpingitis. Over-all clinical efficacy with piperacillin was 96.8 per cent and 90.3 per cent for clindamycin and gentamicin. Fewer bacteria demonstrated in vitro resistance to piperacillin (p = 0.008) and the cost of treatment for these infections was significantly less with piperacillin (p less than 0.05). Serious adverse reactions were not observed with either regimen. Piperacillin provides effective, cost-efficient therapy for women with acute polymicrobial pelvic infections.