In urban environments, pet animals such as dogs and cats may be largely responsible for the progressive increase of zoophilic over anthropophilic dermatophytes in the aetiology of human dermatophytoses. Mapping, in each city, of the natural foci of zoophilic dermatophytes may thus be important for understanding the epidemiology of human dermatophytoses, and for planning preventive measures. We have surveyed dogs and cats suspected of carrying dermatophytic lesions in the Turin area. Hairs, skin scrapings and the contents of pustules or vesicles were inoculated on Dermasel agar supplemented with choramphenicol and cycloheximide. The mating type of the isolates was checked, testing their compatibility with the two mating types of Arthroderma simii Stockdale, Mackenzie and Austwick. We isolated dermatophytes from about 40% of the cases examined. Microsporum canis Bodin was the only dermatophyte found in the lesions. In the cats the lesions were more frequent, in the dogs more severe. Animals less than a year old and male dogs were most often affected. Some cases of transmission of the infection between animals and from animals to man are described. All the isolates of M. canis, tested for mating behaviour, were non-reactive.