Fact-finding surveys of workers occupationally exposed to polychlorinated biphenyls (PCBs) in the production of silk thread or of paint were carried out. Some of the workers showed higher PCB levels in the plasma than typical yusho patients. Gas chromatographic patterns of their PCBs were shown to match the pattern of the PCBs to which they had been exposed. Levels of polychlorinated quaterphenyls in their blood were lower than 0.02 ppb. Medical findings were slight compared with typical yusho patients. From these results, the differences in contamination with PCBs and relevant compounds and in health status between these workers and yusho patients are discussed.