Metronidazole has proven to be a useful and inexpensive antibiotic for the treatment of T. vaginalis and bacterial vaginosis. Few alternatives exist for these two specific indications, and metronidazole will continue to play a primary role in therapy. Oral metronidazole continues to be a very inexpensive alternative to oral vancomycin for the treatment of C. difficile-induced pseudomembranous colitis. For the treatment of moderate to severe mixed aerobic/anaerobic pelvic infections, metronidazole should be considered secondarily in patients who have failed other multiple- or single-drug regimens or in patients who are infected. with anaerobic organisms resistant to other commonly used agents including clindamycin, cefoxitin, cefotetan, or ampicillin/sulbactam. Metronidazole is not a first line drug of choice for antibiotic prophylaxis in obstetric and gynecologic patients.