Polychlorinated biphenyls (PCBs) are widely dispersed in the environment. Occupational exposure to PCBs takes place, e.g., in manufacture and repair of capacitors and transformers. A special type of exposure of workers to PCBs may occur in connection with accidents where capacitors or transformers containing PCBs products are damaged, as in the case of a fire or electric arcing. The quantitation of PCBs poses several problems: There are 209 different homologs and isomers of PCBs. The isomers of PCBs have different responses in the electron capture detector, and the pattern of PCBs in biological specimens is different from that of commercial products. In this study a method was worked out for the analysis of PCBs in serum with the purpose of estimating occupation exposure to PCBs. The PCBs were extracted to an organic solvent, and the extract was purified by use of sulfuric acid and silica columns. Capillary gas chromatography with electron capture detection was used. For separation, temperature programming was used.