Gastric emptying was measured in 9 diabetic patients with autonomic neuropathy (Group 1) and 8 normal controls (Group 2) on 4 occasions after swallowing placebo, 0.5, 1.0 or 2.0 mg of the newly developed prokinetic drug renzapride given double-blind and in random order. The liquid component of the test meal was labelled with In113m and the solid with Tc99m. Liquid emptying was uni-exponential. Solid emptying comprised an initial lag phase, followed by a linear component. Following placebo, the mean lag phase of solid emptying was 40 +/- 7 (S.E.M.) min in Group 1 and 16 +/- 2 min in Group 2 (P less than 0.01). In Group 1 subjects renzapride reduced the mean lag phase by 20-26 min at all doses (P less than 0.01). No effect was seen in Group 2. The linear rate of solid emptying was similar in both groups (0.9 +/- 0.1 and 1.0 +/- 0.2%/min) and was not altered by renzapride. Mean liquid t1/2 was similar in Groups 1 and 2 after placebo (30 +/- 6 and 29 +/- 4 min, respectively) and was decreased with increasing doses of renzapride in both groups. No adverse effects were encountered in any subjects. Renzapride may be useful in the treatment of diabetic gastroparesis.