D ietary carbohydrate accentuation of endogenous triglyceride production has been studied in 33 patients. A broad and relatively continuous spectrum of steady-state plasma triglyceride concentrations was produced in 31 of the 33 subjects during 3 wk of a high carbohydrate (fat-free) liquid formula diet. Two patients developed plasma triglyceride concentrations in excess of 2000 mg/100 ml, and these were the only patients we have studied in which carbohydrate induction of hypertriglyceridemia seemed to be associated with a defect in endogenous plasma triglyceride removal mechanisms. In the remaining 31 patients the degree of hypertriglyceridemia was highly correlated with the insulin response elicited by the ingestion of the high carbohydrate formula (P < 0.005). No significant correlation existed between fasting plasma triglyceride concentration and either plasma glucose or free fatty acid concentrations after the high carbohydrate diet, nor was the degree of hypertriglyceridemia related to degree of obesity. It is suggested that hypertriglyceridemia in most subjects results from an increase in hepatic triglyceride secretion rate secondary to exaggerated postprandial increases in plasma insulin concentration.