SummaryThe immunoreactive insulin response to glucose load has been studied in two patients with pheochromocytoma and carbohydrate intolerance. The results obtained show an impaürement of insulin release with a delayed or absent peak of insulin secretiton before surgery. After the removal of the tumor the glucose tolerance as well as the insulin response improved markedly. These results are commented and compared to similar observations reported in the literature. The inhibition mechanism of insulin secretion in pheochromocytoma is reviewed.