In a prospective study of 109 patients admitted to hospital with a provisional diagnosis of acute stroke, 87 were found to have acute hemiplegic stroke lasting more than 24 hours, and did not have any other co-existing life-threatening disorder. In 81 of these patients, blood glucose and glycosylated haemoglobin (HbA1) were measured at the time of admission. Thirteen of these 81 patients (16%) were hyperglycaemic--in 5 cases, normal HbA1 was found in conjunction with hyperglycaemia suggesting that this represented a 'stress' response. There was no significant difference in age or in blood glucose level between those who died as a result of stroke and those who survived. However, hyperglycaemia with normal HbA1 was demonstrated in 4 of 26 patients who died compared to only one of 55 survivors (P less than 0.02), and all 3 patients with blood glucose greater than 10 mmol/l in conjunction with normal HbA1 died as a result of stroke. Biochemical evidence of 'stress' hyperglycaemia in patients with acute stroke suggests a poor prognosis.