ENDOTHRIX TINEA CAPITIS caused byTrichophyton tonsuranshas been considered an uncommon disease in the northern part of the United States.1In Philadelphia, as in other large northern cities, most ringworm cases have been attributed toMicrosporum audouini,1which produces the typical fluorescent ringworm with which most American physicians are familiar. This paper reports evidence of a significant change in the ringworm flora in Philadelphia based on 44 new cases of endothrix ringworm due to theT tonsuransgroup. Methods All patients with endothrix infection seen at the Skin and Cancer Hospital of Philadelphia from January, 1962 through March, 1964 and at the Dermatology Clinic of St. Christopher's Hospital for Children from December, 1963 through March, 1964 are included in this report. Mycology.— Specimens of hair, scales, and, in some cases, pus were taken from all patients with any inflammatory or noninflammatory scaling disease of the scalp or skin