Yusho type polychlorinated biphenyl (Y-PCB) was prepared in order to study lipid disorder of the PCB poisoning "yusho." Y-PCB caused hypertriglyceridemia and hypercholesterolemia in the rat. Triglyceride lipase (TGL) activities in liver and postheparin serum were suppressed by Y-PCB administration, whereas it was not suppressed in fat. In in vitro experiments, Y-PCB did not suppress TGL in either liver or fat. Although Y-PCB increased fatty acids in the liver 2.5-fold, the relative proportion of fatty acids composition was not changed so remarkably as that in absolute concentrations. These findings suggested that liver is the target of Y-PCB -mediated alteration of lipid metabolism.