A mechanism for the induction of DNA single-strand scissions in cultured Chinese hamster cells by cadmium chloride (CdCl2) was investigated by use of the technique of alkaline elution. Inducibility of DNA single-strand scissions by cadmium was examined under an aerobic or anaerobic culture condition. About 62% of the total cellular DNA was eluted throughout the filter within 10 h of elution time by treatment with 4 X 10(-5) M CdCl2 for 2 h in our usual aerobic medium. In contrast, no difference in elution profiles of DNA was observed between untreated control cells and the cells treated with CdCl2 in the anaerobic medium which was prepared by N2 gas bubbling of aerobic medium for 60 min. Furthermore, elution of DNA from cells treated with cadmium decreased markedly in the presence of superoxide dismutase (SOD) when compared with that in the absence of SOD. Inhibition of the cell growth by cadmium was significantly protected by the presence of SOD in the medium although the cell growth was not restored to the control level. These results indicate that active oxygen species participate in Cd-induced DNA single-strand scissions and also in the growth inhibition of the cells by the metal.