Gastric emptying, mouth-to-cecum transit and whole gut transit of a solid-liquid meal were measured in 43 insulin-treated diabetics and in 30 control subjects by using scintigraphic techniques, the hydrogen breath test and stool markers. In the diabetics various parameters including duration of diabetes, gastrointestinal symptoms and complications such as autonomic neuropathy, peripheral neuropathy and proteinuria were determined and related to gastrointestinal transit times. Gastric emptying was significantly prolonged in diabetics as compared to the control group (p less than 0.05) with 35% of the diabetics disclosing abnormally delayed gastric emptying, whereas no significant overall differences were observed between diabetics and controls concerning mouth-to-cecum transit and whole gut transit time. However, abnormally prolonged mouth-to-cecum transit was detected in 23% and delayed whole gut transit in 26% of the diabetics (p less than 0.02 as compared to the control group). There was a significant correlation of dyspeptic symptoms and diarrhea with prolonged gastric emptying (p less than 0.001). Gastric emptying, but not mouth-to-cecum transit or whole gut transit was significantly related to autonomic nerve dysfunction (p less than 0.001) and peripheral neuropathy (p less than 0.02). Furthermore, gastric emptying and WGT were significantly correlated to proteinuria (p less than 0.03). Using a linear regression model, autonomic neuropathy, diarrhea and dyspeptic symptoms were the major parameters in predicting delayed gastric emptying. It is concluded that in diabetics different compartments of the gut are affected by gastrointestinal motor abnormalities and that these segments are probably regulated by independent or different control mechanisms.