Recent studies suggest that the rate of nutrient transit through the upper gastrointestract may provide cues that are important to the control of food intake. We examined gastrointestinal function in rats with streptozotocin-induced diabetes and related these findings to concomitant changes in food intake. Control and diabetic rats were adapted to one of two isocaloric diets either high in carbohydrate or fat. Control rats ate similar amounts of each diet. In contrast, diabetic animals fed high-carbohydrate diet were hyperphagic, whereas those fed low-carbohydrate diet ate normal amounts of food. Gastric emptying, intestinal mass, disaccharidase activity, and glucose absorption were increased in normophagic diabetic rats fed a low-carbohydrate diet. Feeding diabetic rats high-carbohydrate diet potentiated each of these effects, and food intake was highly correlated with rate of gastric emptying. These and other results indicate that diabetes enhances gastric emptying and intestinal carbohydrate digestion and absorption, even in the absence of hyperphagia. Consequently, the hyperphagia of diabetic rats may be in part a behavioral response to a greatly accelerated clearance of nutrients from the upper gastrointestinal tract that occurs when these animals are fed diets rich in carbohydrate.