We have compared the plasma glucose and immunoreactive insulin responses to oral glucose, intravenous glucose and intravenous tolbutamide of twenty normal subjects with those of eleven patients with chemical diabetes. The two groups were similar in terms of age, sex and degree of adiposity. The insulin response of patients with chemical diabetes was greater at every time interval during all these tests. Thus, we could document no defect in the rapidity of insulin response to these stimuli in patients with chemical diabetes. These results do not support the view that the commonest metabolic abnormality in patients with diabetes is a delay in the insulin response.