OBJECTIVE The effect of erythromycin on gastric emptying is attenuated during hyperglycaemia. The aim of this study was to determine in patients with diabetic gastroparesis whether the effect of cisapride on gastric emptying of solids and liquids is influenced by the plasma glucose concentration. METHODS Nineteen patients with type 1 diabetes mellitus, who had delayed gastric emptying of solids and/or liquids, were studied. On 2 separate days, each patient received cisapride (20 mg) or placebo orally 60 min before scintigraphic measurement of gastric emptying of a mixed solid (ground beef) and liquid (dextrose) meal. The plasma glucose concentrations were measured at -5, 30, 60, 90, and 120 min during each gastric emptying measurement. RESULTS Cisapride accelerated both solid (retention at 100 min 43 +/- 4 vs. 69 +/- 4%, p < 0.001) and liquid (T50 27 +/- 2 vs. 39 +/- 2 min, p < 0.001) gastric emptying. The mean plasma glucose level was not significantly different after placebo when compared with cisapride (19.5 +/- 1.1 vs. 18.2 +/- 1.0 mmol/l). The change in the 50% emptying time (T50) for liquid, but not solid, emptying was related (r = 0.55, p = 0.01) to the change in the plasma glucose AUC from 0 to 30 min between the placebo and cisapride tests, i.e., the acceleration was greater if the plasma glucose concentration was relatively less during the gastric emptying test performed on cisapride. CONCLUSIONS The effect of cisapride on gastric emptying, at least that of liquids, in patients with diabetic gastroparesis appears to be dependent on the plasma glucose concentration.