The secretory aspartic proteinases of Candida albicans and C. tropicalis are potential factors for virulence produced during infection. By indirect immunofluorescence, we have demonstrated proteinase antigen on elements of both species in deparaffinized tissue sections derived from clinical cases of mucosal and deep-seated candidiasis. Occasionally, we observed a halo of fluorescence in the close vicinity of candidal cells, which may reflect secretion of the enzyme. In kidneys, a ring of amorphous fluorescent material surrounding candidal colonies may illustrate alkaline denaturation of secreted enzyme within a pH gradient, which is generated by the fungus. Our findings support the view that candidal proteinase may be a diagnostically relevant antigen.