1. The clinical findings and environmental factors of 138 families infected with Microsporum canis are recorded.

2. Of the 171 children suffering from tinea capitis, 25% had lesions which remained localized, 51% had local spread of infection and 24% had a generalized spread, involving most of the scalp.

3. The clinical pattern of the infection was not associated with the sex or age of the child, nor with the source of infection.

4. In 30.5% of the families there was a definite cat source of infection, in 3.6% a definite dog source and in 13.9% a definite human source. A further 20.3% had a probable animal source, and 7.9% a probable human source, while in 23.9% no obvious source of infection could be found.

5. The social status of 95 families was investigated. In 4.2% the breadwinner was a farmer, in 12.6% he belonged to the professional and managerial group, in 60% he was a skilled labourer and in 22.1% an unskilled labourer. The houses of 75 families were visited. House conditions were classed as good in 58%, fair in 33% and poor in 9%. It is suggested that ringworm due to M. canis in New Zealand is not associated with poverty or poor conditions and no stigma should be attached to the development of an infection.

6. Evidence for the following types of transmission of infection was obtained: cat to child; dog to child; child to child; child to adult; cat to cat; child to cat; dog to cat; cat to dog.

7. The findings of the investigation are discussed. It is suggested that human infections with M. canis are part of a complicated network resulting from the commensal relationship of the cat to man. Better care of cats so that kittens are not allowed to stray would assist in the control of human infections.