Summary The insulin and growth hormone responses to oral glucose load (100 g) in 23 acronaegalic patients, previously treated by external irradiation, are described. Based on current clinical findings, sixteen acromegalics were considered inactive and seven patients active. Two of the latter were treated diabetics. Thirteen healthy, non-obese subjects formed the control group. Five inactive acromegalics had blood glucose values exceeding the upper limits of normal after the glucose load. Both the inactive and active acromegalics had hyperinsulinemia in the fasting state and after glucose load. The observation of an exaggerated serum insulin response to glucose load in clinically inactive acromegalics suggested that chronically elevated levels of circulating growth hormone may have led to permanent changes in the responsiveness of the pancreatic islets to glucose stimulation. The mean fasting value of serum growth hormone was about the same in the controls and the inactive acromegalics; the latter did not show suppression in serum growth hormone levels after glucose load.Research Fellow, Medical Research Council of Canada