A delayed gastric emptying of solids but not of liquids has been recorded in diabetic patients with autonomic neuropathy by radionuclide labelled test meals. Acetaminophen test (rate of acetaminophen absorption after ingestion of 1500 mg of the drug) has been previously validated for quantitative indirect measurement of gastric emptying. In the present study we measured gastric emptying of liquid and solid meals by acetaminophen test in 14 insulin-requiring diabetic patients (7 with and 7 without autonomic neuropathy) and 14 healthy subjects, matched for age, sex, BMI and blood pressure. All values recorded after liquid meal were not significantly different in the three groups of subjects. After solid meal, the mean area under the plasma acetaminophen concentration-time curve was significantly lower in neuropathic diabetic patients vs control subjects (p less than 0.05), and the emptying index (peak time/peak plasma concentration ratio) was significantly higher in neuropathic diabetic patients vs non-neuropathic diabetic patients (p less than 0.01) and vs control subjects (p less than 0.05). These results confirm a delayed gastric emptying of solids but not of liquids in diabetic patients with autonomic neuropathy, and indicate that acetaminophen test may be proposed as simple, safe and noninvasive test for quantitative assessment of gastric emptying in diabetic patients.