To the Editor.— We found that 91 (61%) of 141 cases in a study that were clinically diagnosed as onychomycosis yielded fungi by potassium hydroxide mount or culture, or both. Material from 18 (20%) of these cases failed to yield fungi in culture, although they were shown to contain such organisms in the potassium hydroxide mounts. Trichophyton rubrum was isolated from 16 of the remaining 73 patients; T mentagrophytes from 15; Microsporum canis from six; M gypseum from one; M audouinii from one; Candida albicans from 30; C tropicalis from two; C krusei from one; and C pelliculosa from one. Epidermophyton floccosum was not isolated from any patient. Nail infections from Microsporum sp are exceedingly rare. 1 In our eight patients, only the nails were infected. Five of six patients with M canis onychomycosis and one patient with M audouinii onychomycosis were adults with toenail involvement. These infections involved two