Antioxidants are thought to be important in protecting against damage from active oxygen species. The effects of the antioxidant nutrients vitamins C and E have been investigated after bleomycin treatment in the Salmonella typhimurium bacterial mutation assay, in the human peripheral lymphocyte chromosome aberration assay, and in the mouse micronucleus assay in peripheral blood and bone marrow cells. There were no protective effects from vitamins C and E in the bacterial mutation assay, but vitamin C and not vitamin E abolished chromosome damaging responses in human peripheral lymphocytes, and both vitamins reduced responses in micronuclei from peripheral blood cells in mice. This would suggest that in human cells in vitro and mouse cells in vivo these vitamins could have a protective role.