OBJECTIVES: To evaluate the efficacy of lyophilized lactobacilli in combination with 0.03 mg estriol when compared to metronidazole in the treatment of bacterial vaginal infections. Setting: Multicenter, randomized, single-blind, active-controlled pilot study in 3 independent gynecological practices in Belgium. METHODS: Forty-six, 18- to 50-year-old premenopausal women with a disrupted vaginal flora due to a bacterial vaginal infection (bacterial vaginosis, aerobic vaginitis) were included, provided that fresh phase-contrast microscopy of the vaginal fluid showed lactobacillary flora grade 2B or 3. Patients were given a blinded box with either 12 vaginal tablets of Gynoflor(R) (study medication) or 6 vaginal suppositories containing 500 mg metronidazole (control medication). Eight efficacy variables were studied to assess the status of the vaginal flora at entry, 3-7 days (control 1), 4-6 (control 2) weeks and 4 months after the end of therapy. RESULTS: At control 1, the combined variables equally improved in the lactobacilli group as in the metronidazole group. At control 2, the lactobacillus preparation showed slightly inferior results when compared to metronidazole. At 4 months, this analysis could not be performed due to low numbers, but analysis of recurrence rate and extra medication needed was not different between both groups. CONCLUSION: Lyophilized lactobacilli in combination with low-dose estriol are equivalent to metronidazole in the short-term treatment of bacterial vaginal infections, but have less effect after 1 month. Further studies are required to evaluate the long-term efficacy of lactobacilli when applied repeatedly