Yusho blood and control serum were collected in around 1991 and analyzed for congeners of PCDDs, PCDFs and PCBs. In Yusho blood, TEQ was mainly contributed by 2,3,4,7,8-penta-CDF (77-248 ppt), 1,2,3,4,7,8-hexa-CDF (15-37 ppt) and 2,3,3',4,4',5-hexa-CB (16-77 ppt). Total TEQ in Yusho blood (185-441 ppt) was only 3-14 times higher than that of control serum (31-61 ppt). It is notable that the concentrations of 3,3',4,4',5-, 2,3,3',4,4'- and 2,3',4,4',5-penta-CBs in Yusho blood were comparable to or lower up to 3-5 times than those in control blood.