Sera sent for routine examination from hospitals in south England and Wales were examined and compared with sera from the normal population. Choroiditis was the only disease syndrome showing a significantly higher proportion of positives than normal.Cats were shown to be unlikely vectors of toxoplasma infection, at least by scratching.Thanks are due to many pathologists throughout the country who sent sera and details of cases. Normal children's sera were kindly sent to me by Dr A. D. Evans of the Public Health Laboratory, Cardiff, Dr A. Macrae, Colindale, and Dr Margaret Wilson, Public Health Laboratory, Sheffield. Dr Patricia Bradstreet kindly sent me details of requests for cat scratch antigen.Mr R. Payne carried out the dye tests and Mr H. J. Godwin of the Department of Pure Mathematics, University College of Swansea, kindly checked the statistical calculations.Many thanks are due to Dr R. J. Drummond and his staff of the National Blood Transfusion Service (Welsh Region) for supplying the sera from blood donors.