Structures and concentrations of methylsulphone (MSF) metabolites of polychlorinated biphenyls (PCBs) retained in the liver, lung and adipose tissue of a yusho patient and of a normal person were studied using capillary gas chromatography coupled with electron-capture detection or mass spectrometry. More than 60 isomers of tri-, tetra-, penta- and hexachloro-MSF-biphenyls were detected in the lung of the yusho patient, and the gas chromatographic peaks coincided with those of 40 authentic isomers in retention times by three separate capillary columns, when they were compared with those of 86 synthesized reference compounds. The main components of MSF-PCBs identified in the Yusho patient were 4-MSF-2,5,4'-tri-, 4-MSF-2,5,2',4'-tetra-, 4-MSF-2,5,2',5'-tetra-, 3-MSF-4,5,2',3'-tetra-, 4-MSF-2,5,2',3',4'-penta- and 4-MSF-2,5,2',4',5'-pentachlorobiphenyls, estimated to be 0.7-1.5 micrograms/kg in the lung and 0.3-1.5 micrograms/kg in the adipose tissue.