Only two areas of the world, tropical Africa and New Guinea, are endemic for Burkitt's lymphoma. These are the principal areas of the world where malaria still occurs in hyperand holo-endemic forms, and within these two areas the geographical distribution of the tumour coincides closely with that of endemic malaria. These observations suggest the possibility of a causal connection between chronic stimulation of lymphoid tissue by malaria and the development of the lymphoma (Dalldorf, Linsell, Barnhart, and Martyn, 1964; Edington, Maclean, and Okubadejo, 1964; Burkitt, 1969). Young children with AS haemoglobin (sickle cell trait) are substantially protected against severe falciparum malaria (Allison, 1963). If they could be shown to have a lower incidence of Burkitt's tumour than children with AA haemoglobin, it would provide additional evidence for a role of falciparum malaria in the aetiology of the disease. Williams (1966) compared the haemoglobin electrophoretic patterns of 100 microscopically proven Burkitt's lymphoma patients from Nigeria with those of control children, and he concluded that children with haemoglobin AA were more susceptible to the tumour than those with AS. This paper describes the preliminary results of a patient-control study in Uganda to test this hypo thesis further.