To determine the antagonistic relationship between vaginal lactobacilli and endogenous vaginal microflora.Twenty-two Lactobacillus strains were studied for the production of lactic acid, hydrogen peroxide, and bacteriocin.Under standardized growth conditions, most strains increased their biomass by more than 4 times. Lactobacillus species grew best at a pH > or = 4.5, and growth was retarded at a pH 4.5. The pH of the media is dependent on the cell mass and on all organic acids produced by Lactobacillus species. Although all species produce organic acids, not all produce H(2)O(2) and bacteriocin. Not all strains of G vaginalis can be inhibited by lactobacilli-producing bacteriocin.