The stapes of 6 patients with stapedial otosclerosis was found to contain fungus hyphae (Candida) in the sectioned specimens. The footplate of all cases and the head of the stapes in 2 of the cases revealed single or multiple erosion cavities containing numerous thin branching PAS-positive fungus hyphae with swollen terminal endings and scanty blastospores. Osteoclasts were not observed; occasional osteoblasts, blue mantles and otosclerotic foci were seen. Four patients had been treated for several years with antibiotics and cortico-steroids for recurrent serous otitis media and 1 patient had had frequent catheterization of the eustachian tube. It may be suggested that the Candida infection was a secondary event induced by a general and/or local immunode-pressed condition.