The yeast-like fungi Candida albicans and Candida tropicalis are opportunistic pathogens which are distinguished from less virulent yeasts by the secretion of acid proteases. Candida proteases cleave various human immunoglobulins including IgA2 and secretory immunoglobulins. They cover a wider range of substrates than bacterial IgA-proteases, and possibly play a role in the pathogenesis of thrush and deep candidosis.