Immediate, type I, prick test reactions in man to purified fractions of Candida albicans group A were mediated by different classes of antibody. The allergens were the cell-wall polysaccharide, mannan, and 'purified' cytoplasmic protein fraction, free of mannan, prepared by passage through Sepharose-concanavalin-A. Passive transfer tests in the monkey gave immediate reactions, (1) to the purified, cytoplasmic, protein mediated by heat-labile long-term sensitizing antibody, and (2) to the polysaccharide, mannan, mediated by heat-stable short-term sensitizing antibody.