The infectivity and family incidence of tinea capitis trichophytica have not been clearly established. Children living in a closed institution were experimentally infected with microsporum by Kligman.1Such a procedure does not reproduce the natural epidemiological conditions, nor would it be feasible in the case of trichophyton infections, owing to the need for therapeutic x-ray epilation. A statistical approach seems the only means of clarifying many of the epidemiological problems involved. The records of more than 6,000 cases seen in this department yielded valuable epidemiological information,2but the individual case files did not report the absence as well as the presence of the infection in the rest of the family. Subsequently a special sheet including this information was added to each new patient's file, giving results of both the clinical and microscopical examination of all other family members. This has made