Bacterial vaginosis is characterized by replacement of the normal Lactobacillus-predominant vaginal flora with Gardnerella vaginalis, anaerobic bacteria, and Mycoplasma hominis. The present study evaluated the vaginal flora of women with bacterial vaginosis before and after treatment with intravaginal clindamycin cream. Sixty-seven nonpregnant women with symptoms and signs of bacterial vaginosis, and without other genital tract infections, were randomly assigned to receive placebo cream or 0.1, 1, or 2% clindamycin cream. Quantitative vaginal cultures for facultative and anaerobic bacteria and genital mycoplasmas were performed at enrollment and at 4-7 days and 4-5 weeks after completion of therapy. At enrollment, G vaginalis was recovered from 99%, Bacteroides sp from 94%, Peptostreptococcus sp from 81%, and M hominis from 58% of the 67 women with bacterial vaginosis. The vaginal cultures yielded a median of 12 isolates per specimen, with equal numbers of aerobic and anaerobic species. The mean log concentration was 1.2 X 10(9) cfu/mL for aerobic and 2.6 X 10(8) cfu/mL for anaerobic bacteria. After treatment, the frequency and concentration of bacteria per milliliter of vaginal fluid decreased for G vaginalis, Bacteroides sp, Peptostreptococcus sp, and M hominis. The 2% clindamycin cream had the greatest effect on the bacterial vaginosis-associated flora and resulted in clinical resolution of bacterial vaginosis in 15 (94%) of 16 women. Treatment with lower concentrations of clindamycin cream had less effect on the vaginal flora and resulted in clinical cure in 25 (71%) of 35 women. Therapy was associated with an increase in the frequency and concentration of Lactobacillus, and a probably transient increase in the frequency of Escherichia coli and Enterococcus.(ABSTRACT TRUNCATED AT 250 WORDS)