A B S T R A C TDuring acute hyperglycaemia, gastric emptying is delayed and the compliance of the proximal stomach is increased significantly. It is not known whether the effect of hyperglycaemia on proximal gastric motor function in healthy volunteers results from endogenous hyperinsulinaemia. Therefore we studied the effects of acute hyperglycaemia and hyperinsulinaemia on proximal gastric function, measured using an electronic barostat. Eight healthy volunteers were studied on three separate occasions during : (a) normoglycaemia, (b) hyperglycaemic hyperinsulinaemic clamping, and (c) euglycaemic hyperinsulinaemic clamping. Gastric compliance was significantly (P 0.01) increased during hyperglycaemia (44p5 ml/mmHg), and also during hyperinsulinaemia (38p4 ml/mmHg), compared with during normoglycaemia (31p3 ml/mmHg). During pressure distension, sensations of fullness were greater during hyperglycaemia and during hyperinsulinaemia compared with controls. At a set pressure of minimal distension pressure j2 mmHg, the intrabag volume was significantly higher during hyperglycaemia (292p36 ml ; P 0.05), but not during hyperinsulinaemia (161p35 ml), compared with during normoglycaemia (129p10 ml). Postprandial relaxation was significantly (P 0.01) decreased during hyperglycaemia (93p64 ml) and hyperinsulinaemia (101p64 ml) compared with normoglycaemia (224p56 ml). Thus not only hyperglycaemia, but also hyperinsulinaemia, influences proximal gastric compliance, postprandial relaxation and symptom perception.