Experimental euglycaemic hyperinsulinaemia (insulin levels 46 +/- 4 mU/l) impaired the post-absorptive gastrointestinal motility in healthy individuals; the effect being particularly pronounced in the upper gastrointestinal tract (stomach and proximal duodenum). The postprandial gastric emptying, measured with a standardized 99mTc labelled meal, was also significantly delayed (t50 increased by 38% or 32 min). This was combined with a slower carbohydrate absorption (delay in peak blood glucose level about 40 min). Furthermore, during experimental hyperinsulinaemia higher blood glucose levels were seen at 120 min than at 60 min after food ingestion. This was not seen in any subject in the control study where only 0.9% NaCl was infused. Blood levels of the motility-stimulating hormone, motilin, were significantly lower during experimental hyperinsulinaemia. Thus, experimental hyperinsulinaemia impairs the gastrointestinal motility in both the postabsorptive and postprandial states. This effect is combined with a delayed carbohydrate absorption. Hyperinsulinaemia per se may thus lead to alterations in carbohydrate absorption and can also contribute to the gastrointestinal disturbances in diabetes.