Leukocyte counts and body temperature were studied in 232 untreated Burkitt's lymphoma patients. Differential counts were obtained in 153 of them. There was no significant diagnostic variation in circulating leukocyte levels and no correlation between the size, site, or stage of the tumour and leukocyte counts or body temperature. No explanation can be given for low neutrophils in 40 of the 153 patients whose differential counts were performed.