Further investigations on the reduction of vitamin A content in the liver of rats fed a 0.1% PCB diet were conducted. The first experiment, in which rats were fed a 0.1% PCB diet for 8 weeks and vitamin A in the liver was determined at 2-week intervals, suggested that a significant decrease of vitamin A in the liver might occur within 2 weeks of PCB ingestion. In the second experiment a significant reduction of vitamin A content per gram of liver, but not per whole liver, in rats fed a 0.1% PCB diet was observed on the 3rd day of PCB ingestion, and then on the 6th day the difference between the control group and the PCB-fed group became much more remarkable. But thereafter no further reduction was seen, indicating a lower limit of vitamin A concentration in the liver of rats fed PCB. It was found that retinol binding protein in the serum of rats fed the 0.1% PCB diet decreased to one-half that of the control group on the 10th day of PCB ingestion, suggesting also a marked reduction in serum vitamin A level. Another experiment revealed that a decrease in hepatic vitamin A occurred even at low PCB levels, but serum phospholipid did not respond at all to any PCB level examined until 7 days after PCB ingestion began. The mechanisms of sensitive response of vitamin A in the animals fed PCB are briefly discussed.