Ringworm in cats is a common dermatological disorder of public health importance. Investigations in this country 3,7 and other parts of the world 5,6 have disclosed that Microsporum canis is the principal cause of this condition in cats. In a recent survey 3 of ringworm of animals in the United States, this fungus has been found to be responsible for approximately 98% of the feline cases studied. Such infections are frequently transmitted to human contacts, and infected cats constitute the principal source of this agent for man. M. canis is also an important cause of dermatophytosis in dogs, pet monkeys, and horses, 3 and such lower-animal hosts are also frequently involved in the transmission of the disease to humans. Although it has been conclusively established that the relatively common M. canis ringworm in man represents spread from cats and other animals, to date no attempts have been made in this