Abstract Amifostine is the most effective radioprotector known and the only one accepted for clinical use in cancer radiotherapy. In this work, the antigenotoxic effect of amifostine against γ‐rays was studied in Escherichia coli cells deficient in DNA damage repair activities. Assays of irradiated cells treated with amifostine showed that the drug reduced the genotoxicity induced by radiation in E. coli wild‐type genotypes and in uvr , recF, recB, recB‐recC‐recF mutant strains, but not in recN defective cells. Thus, the mechanism of DNA protection by amifostine against γ‐radiation‐induced genotoxicity appears to involve participation of the RecN protein that facilitates repair of DNA double‐strand breaks. The results are discussed in relation to amifostine's chemopreventive potential. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2010.