A prospective, randomized, nonblind study was performed to compare the efficacy of a 7-day vaginal regimen with 500 mg metronidazole (Flagyl) once a day and that of oral treatment with 400 mg metronidazole twice daily for 7 days in the treatment of nonspecific bacterial vaginosis. No treatment was given to the sexual partners and there was no restriction of sexual intercourse. 38 women completed the study and at follow-up after 4 weeks, women receiving vaginal therapy had a cure rate of 79% compared with 74% in the women on oral therapy. Cure rates were lower among users of an intrauterine contraceptive device (57 versus 88% among nonusers). The occurrence of lactate-producing bacteria (lactobacilli and aerobic streptococci) in the vagina was significantly higher in women after vaginal compared with oral therapy. Gardnerella vaginalis was isolated in 58% of the women after vaginal and in 44% of the women after oral treatment. It is concluded that vaginal application of 500 mg metronidazole daily for 7 days is equally effective as oral administration in the treatment of bacterial vaginosis.