Findings on the effects of GIP indicate that its incretory effect on stimulation of insulin secretion under conditions of hyperglycaemia is more important than the formerly known effect of enterogastrone. Numerous experimental trials provide evidence that GIP can participate in the regulation of the postprandial glucose and lipid metabolism and circulation in the splancnic area. The physiological action of GIP has however still obscure consequences in pathological conditions. Because GIP secretion by the mucosa of the small intestine is conditioned by nutrient absorption and its incretory effect on the functional capacity of the B-cells of the pancreas, it is assumed that it is of clinical importance in diseases of the digestive tract and in metabolic disorders. The author presents a review of recent findings on GIP and its action in diabetes, obesity, chronic pancreatic disease and other pathological conditions. In view of the controversial reports the clinical importance of GIP is not quite clear so far.