BACKGROUND Gastrointestinal motility disorders are common in patients with diabetes mellitus. Recent studies indicate that hyperglycemia can affect gastric emptying and gastric motility in healthy subjects and diabetics. METHODS The effect of acute hyperglycemia on gastrointestinal motility was studied with a manometric technique in healthy subjects. Seven individuals, four men and three women, 23-34 years old, were studied on 2 different days. On 1 of the days a 5-h registration was performed after an overnight fast. On another day and after an initial basal period, acute steady-state hyperglycemia was induced by intravenous glucose infusion for 90 min. Motility variables were evaluated in four segments: in the gastric antrum, the proximal duodenum, the distal duodenum, and the proximal jejunum. RESULTS Fasting migrating motor complex rhythm including migration of phase III prevailed during hyperglycemia. Compared with euglycemia, the motility index in phase II was lower during hyperglycemia in all segments studied. In the antrum the difference was 62% (p < 0.01); in the proximal duodenum, 37% (p < 0.01); in the distal duodenum, 44% (p < 0.05); and in the jejunum, 58% (p < 0.01). During hyperglycemia the prevalence of propagated contractions in phase II was significantly lower than during euglycemia both in the antrum and the proximal duodenum. In the last part of phase III in proximal duodenum most individual contractions were propagated in orad direction compared with early phase III, and this difference persisted during hyperglycemia. The number of long clusters was significantly increased during hyperglycemia as compared with euglycemia: 2.0 +/- 0.6 per hour versus 0.4 +/- 0.14 (p < 0.01). In late phase II plasma levels of motilin and pancreatic polypeptide were significantly decreased during hyperglycemia. CONCLUSIONS Hyperglycemia not only reduces the motility in the stomach but also inhibits motility in both the duodenum and the jejunum. The results show that acute hyperglycemia has an important impact on small-intestinal motility.