During 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 (44±5 ml/mmHg), and also during hyperinsulinaemia (38±4 ml/mmHg), compared with during normoglycaemia (31±3 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 +2 mmHg, the intrabag volume was significantly higher during hyperglycaemia (292±36 ml; P < 0.05), but not during hyperinsulinaemia (161±35 ml), compared with during normoglycaemia (129±10 ml). Postprandial relaxation was significantly ( P < 0.01) decreased during hyperglycaemia (93±64 ml) and hyperinsulinaemia (101±64 ml) compared with normoglycaemia (224±56 ml). Thus not only hyperglycaemia, but also hyperinsulinaemia, influences proximal gastric compliance, postprandial relaxation and symptom perception.