Octachlorostyrene (OCS) is a persistent and bioaccumulative toxicant (PBT) that is a halogenated aromatic compound. OCS belongs to the primary level I group chemicals designated by the US Environmental Protection Agency, which are the most concerning chemicals among the PBTs. It is known that OCS has never been commercially used but has been widely distributed in the environments. Although OCS has been occasionally measured in human samples as well as environmental samples such as water, soil, sediment, fishes, and marine mammals, the impact of OCS on human health is still unclear. It is assumed that the toxicities of OCS follow the other chlorinated chemicals, like hexachlorobenzene, and there is also possibility to be metabolized to generate radicals. In this study, cell toxicity and induction of reactive oxygen species (ROS) by OCS (6.25, 12.5, 25, 50 microM) were studied in cultured human Chang liver cells. Exposure of cultured cells to OCS led to cell death, ROS increase, and cytosolic caspase-3 activation. ROS increase was related to the decreased level of GSH. Chromatin fragmentation and condensation were also shown in OCS-treated cells. These results suggest the toxicity in the human Chang liver cells by OCS may be induced through the apoptotic processes.