Bacterial vaginosis (BV) is a condition whose prevalence has been reported at 29% and whose adverse effects are becoming more and more recognized. Current antibiotic treatment often does not cure the infection, nor prevent relapses. The recent clinical finding that probiotic lactobacilli can augment antibiotic efficacy was investigated in a series of in vitro studies. Gardnerella vaginalis ATCC 14018, an organism associated with BV, and probiotic Lactobacillus rhamnosus GR-1 as well as freshly isolated Lactobacillus plantarum KCA were dispensed into microplates containing different concentrations of metronidazole ranging from 0 µg/ml as control to 8000 µg/ml. Growth of the strains was markedly inhibited at high antibiotic concentrations, but a significant (p=0.005) stimulatory effect occurred for L. rhamnosus GR-1 at 64 µg/ml and 256 µg/ml (p=0.02). After the organisms entered stationary phase, the stimulatory effect declined. At concentrations ≥4000 µg/ml, there was marked growth inhibition of more than 71% on the two lactobacilli strains, while Gardnerella vaginalis was inhibited over 70% at ≥3000 µg/ml. The surprising ability of probiotic lactobacilli to survive and grow in metronidazole may have implications for complimentary probiotic and antibiotic therapy of BV.