Hydrogen ion concentration in a medium in which the adherence of group B streptococci to vaginal and buccal cells takes place, significantly influences the reaction intensity. At physiological pH, group B streptococci adhere significantly more weakly than at pH 5.5 to buccal epithelia, and at pH 7.2 to vaginal epithelia. Thus at nonphysiological pH values the percentage of adherent cells is markedly higher.