We assessed gastrocolic transit time in 10 diabetic patients with autonomic neuropathy and 10 healthy age-matched controls by measuring breath hydrogen rise and scintigraphic bolus progression after ingestion of an isosmotic lactulose solution containing 99m-Tc-diethylentriamine-pentaacetic acid. Mean transit time in diabetics with autonomic neuropathy was significantly slower with respect to controls, with a good correlation between the two techniques. Moreover, diabetics had a significantly shorter discharge time (defined as the period that elapses between the arrival of the meal into the cecum and the hydrogen increase in the expired air). It is concluded that the selective lipid malabsorption seen in diabetic patients could be the result of cecal-ileal reflux, as a contaminating consequence of the last ileal loop. A possible motor innervation defect of the ileo-cecal valve is postulated in these subjects.