Nine strains, isolated from leukoplakias or normal mucosa of the oral cavity, and representing the species Candida albicans, C.tropicalis, and Torulopsis glabrata were tested for the capacity to degrade IgA1, IgA2, and S-IgA in liquid cultures. IgA fragments were characterized by SDS-PAGE of culture supernatants in combination with immunoblotting analysis using antibodies specific for heavy chain and light chain determinants. Strains of C.albicans and C.tropicalis were found to express stronger proteolytic activity than a strain of T.glabrata. The three types of IgA were all degraded, alpha-chains being the primary targets. Immunoblotting analysis indicated that divalent fragments corresponding to the deletion of one or both of the Fc alpha constant domains (F(abc)2 alpha or F(ab)2 alpha) were produced. Monovalent half-molecules corresponding to these fragments could also be detected, suggesting that the yeast strains were capable of cleaving inter-alpha-chain disulphide bridges. The possible consequences of yeast-induced degradation for the function of IgA antibodies are discussed.