A prospective study of the socio-economic status and physical growth of seventy-six children aged 3-10 years, with Burkitt's lymphoma (BL), has revealed that most of the patients were from the lowest socio-economic classes. Majority of the fathers were farmers, labourers or petty traders. The BL children were, as a group, significantly lighter in weight and shorter than controls. It is postulated that although the weights were probably adversely affected by the illness itself, the shorter heights which were most likely present before the onset of the illness, indicated chronic undernutrition. This, together with a low level of immunization would predispose the children to frequent infections, including malaria. Frequent infections would thus condition the reticuloendothelial system to be more susceptible to the lymphoproliferative properties of the EB virus, resulting in malignant changes such as Burkitt's lymphoma.