A histopathological and histochemical evaluation of biopsy material from 53 patients with tinea capitis due to Microsporum audouini, Trichophyton schoenleini, Trichophyton tonsurans, Trichophyton sulfureum, and Trichophyton violaceum shows fungal elements rich in polysaccharides. An abundance of hyaluronic acid is present in the stroma, in the outer root sheath of anagen hair follicles, and around the fungal elements in M audouini and T schoenleini infections. It is shown that the latter two organisms cause endo-ectothrix infections, and the other dermatophytes in the study are true endothrix parasites. Observations suggest that the survival and propagation of the dermatophytes is pH dependent, and this may be related to the presence of large amounts of hyaluronic acid. The noninflammatory clinical appearance of infections due to M audouini contrasts sharply with the intense histopathologic changes.