The metabolism of acetate-U-14C and L-alanine-U-14C in carp was investigated. On feeding a high carbohydrate diet, incorporation of radioactive carbon from these labeled compounds into hepatopancreatic lipid was decreased, whereas 14CO2 evolution was increased. The condensing enzyme activity was also depressed. The reverse of these phenomena was observed on feeding a high protein diet. Gluconeogenesis appeared to proceed more from 14C-alanine than from 14C-acetate. GPT and GOT activities were almost equal, regardless of dietary conditions. However, G6Pase activity increased with an increase in dietary protein. The results obtained suggest that the glycolytic activity of carp is not contributive enough to synthesize lipid. The precursor for lipogenesis seems to be citrate formed when amino acids are actively metabolized through the TCA cycle. The energy-utilization form of normal carp seems to resemble that of diabetic animals. Possible relationships between carbohydrate, protein and lipid metabolism and the inferiority of carbohydrate as an energy source in carp are discussed.