The polychlorinated quaterphenyl (PCQ) concentrations in the blood are important discriminative parameters in Yusho patients. In this study, the analytical method of PCQ was improved, and a high speed and precision analysis could be achieved. A recovery test showed satisfactory recoveries of 99.5% (RSD4.8%, n = 5). Using this method, the authors analyzed 62 blood samples which were collected from the 2004 annual inspection for Kanemi rice oil poisoning. PCQ was detected in 20 blood samples (ranging from 0.03 to 4.15 ng/g). The average concentration was 2.07 ng/g in the pattern A (typical Yusho patients), 0.76 ng/g in the pattern B, 0.18 ng/g in the pattern BC and 0.01 ng/g in the pattern C, respectively.