The effects of feeding different carbohydrates on hepatic gluconeogenesis in BHE rats was studied. Three experiments were conducted that differed only in the aspects of gluconeogenesis examined. In experiment 1, gluconeogenesis and ketogenesis by hepatocytes isolated from 48-h starved rats were determined. In experiment 2, the activities of selected gluconeogenic enzymes were determined in starved and nonstarved rats. In experiment 3, the levels of the various metabolites of glycolysis and the citric acid cycle were determined in nonstarved rats. Rats were fed diets containing starch, maltose, glucose, sucrose or an equimolar mixture of glucose and fructose. In starved rats, gluconeogenesis was less in starch-fed rats than in rats fed any of the sugar diets. These same diet differences, with few exceptions, were also observed in ketogenesis. Glucose 6-phosphatase activity was lower in nonstarved rats fed starch and maltose than in rats fed glucose, sucrose, or glucose and fructose. These same nonstarved rats also had lower phosphoenolpyruvate carboxykinase and higher glutamate pyruvate transaminase activities than rats fed the other diets. In the starved rats, the diet differences were erased. Starved rats had lower activities of these gluconeogenic enzymes than nonstarved rats. Diet differences in the levels of the different metabolites in nonstarved rats were observed. The results show that dietary carbohydrate can influence gluconeogenesis. However, the mechanism of their effect is as yet unknown.