Induction of Chromosome Aberration and Sister Chromatid exchange by CdC1₂ in CHO-K, cells and human peripheral lymphocytes was studied in order to compare the applicability of them for the assessment of cytotoxicity of cadmium. The frequencies of chromosome aberrations in CHO cells treated with cadmium during G₁ and human lymphocytes during G_0 were increased with dose-dependent manner, and almost all aberrations were chromatid types suggesting that cadmium was S-dependent agent. On the other hand, no significant increase in frequencies of SCE both in CHO cells and in human lymphocytes was observed. These data implicate that chromosome aberration analysis is good for the assessment of cadmium toxicity but SCE analysis is not good for it.