AbstractPolychlorinated biphenyl (PCB) and polychlorinated quaterphenyl (PCQ) concentrations in the blood and subcutaneous fat tissue from 11 patients with PCB poisoning (Yusho) and 10 controls were analyzed by electron captured gaschromatography. The mean concentration levels of blood PCB and PCQ and the CB% ratio were elevated in patients with Yusho. The PCB pattern was the A type in 5 cases and the B type in 6 others. The mean concentration level of PCB in subcutaneous fat tissue was 1579.45 ppb in the Yusho group, 3.9 times higher than that in the control group. The mean concentration level of PCQ was 206.65 ppb, 119 times higher than that in the control group. The mean value of CB% was 3.22 in the Yusho group and 0.66 in the control group. These results show that PCB and PCQ accumulate in the subcutaneous fat tissue of patients with PCB poisoning (Yusho), as late as 17 years after diagnosis of the disease. The PCB and PCQ concentration levels in the subcutaneous fat tissue appear to be useful in diagnosis and evaluation of prognosis in this disease. Investigations of the elimination of PCB and PCQ in subcutaneous tissues should be done.