Insulin secretion following the intravenous injection of 75 units of secretin was studied in 8 non-obese diabetics of various types. Six of these patients were also tested by intravenous injection of 25 g of d-glucose. While the secretion of insulin was greatly reduced following stimulation with glucose, it was normal or greater than normal following the administration of secretin. This is taken to indicate that while the release of insulin from the β-cell into the blood stream is normal in the diabetic organism, it is the glucose metabolism in the β-cell that is disturbed.