Epidemiological surveillance of Creutzfeldt-Jakob disease (CJD) in the UK identified 21 patients who had received a blood transfusion and 29 who had donated blood, out of a total of 202 definite and probable cases. This frequency of blood transfusion or donation did not differ from that in age and sex matched controls, and the clinical features in patients with a history of blood transfusion were similar to those of classical CJD and clearly distinct from CJD in recipients of human growth hormone. This evidence does not suggest that blood transfusion is a major risk factor for CJD.