Nonspecific vaginosis (NSV) is a very common clinical syndrome with characteristic clinical, biochemical, and microbiologic features. There is a thin, malodorous homogeneous, grey, nonpurulent vaginal discharge. The discharge usually has a pH greater than 4.5, contains "clue cells" on wet mount examination, and produces a "fishy" odor when mixed with 10% potassium hydroxide. The discharge contains an increased concentration of at least seven amines which are presumably produced by bacterial decarboxylases; and several volatile and non-volatile organic acid metabolites of anaerobic bacteria. Although the pathogenesis of NSV is not understood, the normal, lactobacillus-dominated microbial flora is replaced by Gardnerella (Haemophilus) vaginalis and certain anaerobic species. Treatment with sulfonamide creams or oral tetracycline is usually ineffective. Ampicillin is often effective, but metronidazole appears to be the most effective antimicrobial for this condition. The optimal dose of metronidazole, and the need for treatment of sex partners, require further study.