Reactive oxygen species play an important role in the mediation of cell killing. But the mechanistic links between reactive oxygen species (ROS) and cell death remains unclear. There was a speculation that ROS, especially hydroxyl radicals can induce necrosis but not apoptosis in cells treated with copper-1,10-phenanthroline, IICu(OP)(2). In this paper, liver carcinoma cell line (Bel-7402) was treated with IICu(OP)(2) and its effect was examined by several means. Cells were found to undergo changes characteristic of apoptosis. Hoechst staining showed apoptotic body appeared in the cells induced by IICu(OP)(2). When DNA extracted from the cells treated with IICu(OP)(2) was analyzed by agarose gel electrophoresis it generated 'ladder' pattern of discontinuous DNA fragments. Sub-G(1) peak was detected in treated cells. Furthermore, two different flow cytometric methods were used, each allowing us to relate the apoptotic cells to the position the cell-cycle position. Apoptosis induced by IICu(OP)(2) was limited to G(1)-phase cells. Using cyclin analysis, the expression of cyclin E in G(1) was blocked. Thus, it was concluded that IICu(OP)(2) can induce G(1)-phase specific apoptosis in Bel-7402.