The present experiment was carried out to examine the mechanism of cytotoxicity of Chromium in CHO cells. Chromium induced chromosomal aberrations in a dose-dependent manner. The most frequent type of aberration was chromatid deletions and chromosome type exchanges were also observed. Ultrafiltrates of culture media from CHO cells treated with Chromium induced sister chromatid exchanges(SCE) in CHO cells and Chromium induced lipid peroxidation. It was suggested that indirect effect through formation of clastogenic factor(CF) as well as direct effect on DNA might contribute to the cytotoxicity of Chromium.