We investigated the effects of glycerol monolaurate (GML) on Lactobacillus, Candida, and Gardnerella vaginalis human vaginal microflora. Our previous work demonstrated that 6 months of GML treatment vaginally does not alter lactobacillus counts in monkeys. Candida and G. vaginalis are commonly associated with vaginal infections in women, many becoming chronic or recurrent. In vitro growth inhibition studies determined the effects of GML (0 to 500 g/ml) against multiple Candida species and G. vaginalis. A randomized, double-blind study investigated the effects of GML on vaginal microflora Lactobacillus, Candida, and G. vaginalis in colonized or infected women (n ؍ 36). Women self-administered intravaginal gels containing 0% (n ؍ 14), 0.5% (n ؍ 13), or 5% (n ؍ 9) GML every 12 h for 2 days. Vaginal swabs were collected before and immediately after the first gel administration and 12 h after the final gel administration. Swabs were tested for Lactobacillus, Candida, G. vaginalis, and GML. In vitro GML concentrations of 500 g/ml were candicidal for all species tested, while a concentration of 10 g/ml was bactericidal for G. vaginalis. Control and GML gels applied vaginally in women did not alter vaginal pH or Lactobacillus counts. Control gels reduced G. vaginalis counts but not Candida counts, whereas GML gels reduced both Candida and G. vaginalis. No adverse events were reported by participating women. GML is antimicrobial for Candida and G. vaginalis in vitro. Vaginal GML gels in women do not affect Lactobacillus negatively but significantly reduce Candida and G. vaginalis.The human vagina is colonized by microbes, and infections occur when the balance is disturbed. Under healthy conditions, vaginal flora is dominated by lactobacilli, which maintain acidic pH through production of organic acids at times other than menstruation (1,8,13,30). Disruptions of vaginal pH or lactobacilli may allow potentially pathogenic microorganisms to grow and dominate.Bacterial vaginosis (BV) is a common chronic infection characterized by complex vaginal flora changes, which include elevations of vaginal pH and, when symptomatic, malodorous discharge and inflammation (2,5,11). BV is associated with preterm delivery, increased risk of HIV transmission, and risk of other infections (17). The prevalences of BV range from 4 to 40% of women, with the highest prevalence among patients at sexually transmitted infection clinics (25). During BV infection, there are reductions in lactobacilli and increases in bacterial groups such as the Gram-negative bacterium Gardnerella vaginalis (3,10,18,25). Additional bacterial groups that are associated with BV include Bacteroides fragilis and Peptostreptococcus (12, 28). Current treatment recommendations for BV include metronidazole and clindamycin (4).Vulvovaginal candidiasis (VVC) is also a common infection. VVC is caused by Candida species, most often Candida albicans (7,26). It is estimated that 70 to 75% of women experience VVC at least once during their reproductive years (14), and 5 to 8...