The prevalence of nonspecific vaginitis was 24% among 98 randomly selected women examined at a clinic for sexually transmitted diseases and 32% among 135 women with suspected cervicitis at the same clinic. Mycoplasma hominis was isolated more often and serum antibody levels to M. hominis were higher in women with nonspecific vaginitis than in women without nonspecific vaginitis. Similarly, the rate of isolation of Gardnerella vaginalis and the quantitative growth of G. vaginalis were higher for women with nonspecific vaginitis. Abnormal results of gasliquid chromatographic analysis of vaginal fluid and the presence of abnormal diamines in the vaginal fluid also were associated with nonspecific vaginitis and with the isolation of M. hominis, whether or not G. vaginalis was isolated. Further studies of the ecologic interactions among M. hominis, G. vaginalis, and anaerobes in nonspecific vaginitis are needed for a better understanding of the pathogenesis of this syndrome.