167 patients suffering from nonspecific bacterial vaginoses were vaccinated in a double-blind, randomized, placebo-controlled trial. It appeared, during the study period of 14 months, that the vaccination with Gynatren, a lactobacillus vaccine, was significantly better than the placebo as concerns its therapeutical effect, but mainly as concerns its preventive effect (less reinfections). The vaccine was very well tolerated. We conclude that vaccination with Gynatren is an effective measure to prevent recurrences of nonspecific vaginosis.