1. By the dye test, toxoplasma antibodies in titres of 1/4 or more, were found in the sera of 25% of a sample of adult population of Sheffield.
2. Significantly higher, when strength as well as number was considered, were the reactions of the sera of veterinary surgeons and abattoir workers.
3. Still higher were the reactions of the sera of those who handled rabbits. Highest of all were those of rabbit trappers.
4. Toxoplasma antibodies active to a titre of 1/40 in the dye test were found in 34% of wild rabbits and, to a titre of 1/160, in 5%.
Thanks are due to the hundreds of volunteers who made the survey possible. The Medical Officers of Health of Sheffield, Leeds and Manchester and the veterinary officers, superintendents of markets and food inspectors in these cities made admirable arrangements, which are gratefully recorded, for the obtaining of specimens. Valuable advice and help in obtaining samples from rabbits were given by officers of the Pests Control Division of the Ministry of Agriculture and Fisheries and by their trappers. Dr Marmion supplied some of the sera from veterinary surgeons. The assistance of the technical staff of the Bacteriology Department, University of Sheffield, is gratefully acknowledged. The work was assisted by a grant to C.P.B. from the Medical Research Council.