Clumping of Candida albicans occurred when the organisms were incubated in normal human serum. This clumping of yeast and mycelia apparently accounts for the decrease in colony-forming units previously described. Homogenization of serum after incubation showed that clumping did not bring about organism death. Clumping of C. albicans did not occur in sera from three patients with chronic mucocutaneous candidiasis and furthermore these sera inhibited clumping in normal sera. The inhibitor of clumping present in the sera of patients with chronic mucocutaneous candidiasis has been identified as specific IgG C. albicans antibody.