The changes of lipid metabolism in carp caused by feeding a PCB diet were as follows. 1) In in vivo experiments, total lipid and triglyceride in the carp hepatopancreas increased slightly, and glycogen decreased. 2) In in vivo experiment, the rate of incorporation of 1-¹⁴C-palmitate into the hepatopancreatic lipid fractions did not change, but the incorporation of radioactivity into blood-plasma lipid increased in the triglyceride and free fatty acid fractions, and decreased in the phospholipid and free cholesterol fractions. 3) In in vitro experiments, the incorporation of 1-¹⁴C-palmitate into lipids of the hepatopancreas increased slightly in the triglyceride fraction, especially in the α, α'-position of the triglyceride. 4) The triglyceride synthetase and α-glycerophosphate dehydrogenase activities in hepatopancreas were slightly increased by PCB administration. The changes of lipid metabolism in the carp hepatopancreas on PCB administration are discussed in comparison with those in mammals.