1. Two hundred and ten blood samples were obtained from workers in the fish trade. Of these, fifty-one, or 24·2 per cent., gave positive sero-reactions in dilutions of the serum ranging from 1/30 to 1/1000.

2. There was no significant difference in the number of positive sero-reactions occurring in male or female workers.

3. In a control series of 406 blood specimens from individuals not engaged in the fish trade, no positive sero-reactions were obtained.

4. Evidence is adduced that leptospiral infections occur in three grades: (a) severe infections associated with jaundice; (b) mild infections with pyrexia and no jaundice; and (c) latent or inapparent infections with no clinical manifestations.

5. Preventive methods have been detailed which, if put into practice, would, it is believed, reduce the incidence of this disease.

6. Sufficient evidence has been produced to show that this disease is occupational in nature, and as such should be scheduled under the Workmen's Compensation Act.

Acknowledgements. We are indebted to Drs Hill, Goldie and Fullerton of the Department of Medicine for much help in the collection of specimens.