Two biochemical indicators of bacterial vaginosis, proline aminopeptidase activity and gas-liquid chromatographic analysis, were compared. Five hundred women had their vaginal secretions tested for pH, presence of a positive amine test, levels of volatile and nonvolatile short-chain organic acids, and proline aminopeptidase activity. In addition, direct microscopic and Gram stain examinations were performed. Of the 500 women, 349 (70%) had some form of vaginitis. One hundred sixteen were diagnosed as having bacterial vaginosis, and 69 of these (59%) had Mobiluncus sp on either direct microscopic or Gram stain examination. Two hundred thirty-three had either mixed or other forms of vaginitis. One hundred fifty-one patients were normal. The sensitivity of the proline aminopeptidase assay was 83 and 79%, respectively, in patients having bacterial vaginosis with and without Mobiluncus morphotypes. In contrast, gas-liquid chromatography of short-chain organic acids had sensitivities of 71 and 30%, respectively. Specificity of both assays was about 95%. The greater sensitivity of the proline aminopeptidase assay, especially in patients without Mobiluncus morphotypes, proves its superiority.