In a randomized, double-blind clinical trial from general practice, 500 mg metronidazole pessaries applied once daily for seven days were compared with placebo in the treatment of bacterial vaginosis. Seventy-five women completed the study. At the follow-up visit immediately after completion of treatment, none of the patients on metronidazole fulfilled the criteria for bacterial vaginosis, compared with 12 (35%) in the placebo group (p less than 0.001). Nine (22%) of the patients treated with metronidazole harboured Gardnerella vaginalis after treatments, compared with 31 (91%) in the placebo group (p less than 0.001). Symptoms had improved or disappeared in 33 (80%) on metronidazole, and in 18 (53%) on placebo therapy (p less than 0.05). Four weeks after the follow-up visit, symptoms were reported by 28% in the metronidazole group and by 44% in the placebo group (p greater than 0.05). Metronidazole pessaries are effective in the treatment of bacterial vaginosis.