The relationship between polychlorinated biphenyl (PCB) and polychlorinated quaterphenyl (PCQ) concentrations in the blood and hair was investigated. The materials in this study consisted of 49 blood samples and hair obtained from 27 patients with PCB poisoning (Yusho) and 22 normal controls. The alkaline decomposition method described in the official standard analytical methods for the isolation of PCB and PCQ fractions was used. In the blood of the control group, the mean concentration of PCBs was 2.25 ppb, while the concentration of PCQs was too low to be detected by our analytical method. On the other hand, the mean concentration of PCBs in the Yusho group was about 2.8 times higher than that in the control group. The mean concentration of PCQs in the blood was 0.61 ppb in the Yusho group, but PCQs were not detectable in the control group. In the hair, the mean concentration of PCBs was 25.85 ppb and 9.41 ppb in the Yusho group and control group respectively. The mean concentration of PCQs in the hair of Yusho patients was 0.44 ppb, but PCQs were not detected in the control group. The PCB level in the hair was higher than that in the blood, but the PCQ level in the hair was lower than that in the blood. These results suggest a difference of excretory system among polyhalogenated compounds such as PCBs or PCQs. We consider that PCBs display a greater affinity than PCQs for the pilosebaceous system of the human skin.(ABSTRACT TRUNCATED AT 250 WORDS)