Fasting serum aminograms were studied in rats fed a commercial stock diet or purified diets supplemented with or without 1% cholesterol and 0.25% sodium cholate. Sucrose, glucose or fructose served as a carbohydrate source for each purified diet. Accompanied by marked rises in serum cholesterol, the serum amino acid profile of rats fed glucose or fructose diets was modified significantly by dietary cholesterol. On feeding a glucose diet, dietary cholesterol caused decreases in Trp, Thr and Tyr and increase in Pro and Met. However, the concentration of total essential amino acids remained unchanged. Feeding a fructose diet resulted in a significant reduction of the amino acid level in comparison with that observed with glucose. This decrease was routinely compensated by the inclusion of cholesterol in the diet with the concentration of a number of amino acids being increased. Only Trp was decreased by this dietary manipulation. The serum aminogram of rats fed either a commercial stock diet or a sucrose diet was inconsiderably modified by dietary cholesterol. These data denote that dietary cholesterol influences the metabolic process of amino acids and that the response to cholesterol is modified by the carbohydrate source of the diet.