Zearalenone (ZEN) is a non-steroidal estrogenic mycotoxin produced by Fusarium fungi. It contaminates different components of the food chain and can cause serious economic and public health problems. The major metabolites of ZEN in various animal species are alpha- and beta-zearalenol (alpha-, beta-ZOL). Some in vivo studies have shown that these two metabolites are as toxic as the mother molecule (ZEN), but other investigations have demonstrated that alpha- and beta-ZOL are less toxic than ZEN. Thus, the aim of the present study was to evaluate cytotoxicity and genotoxicity of alpha- and beta-ZOL in vivo, in mouse bone-marrow cells and in vitro, in cultured HeLa cells, and to compare it with ZEN. ZEN showed the same cytotoxicity as alpha-ZOL and both are more cytotoxic than beta-ZOL. Genotoxicity of ZEN and its derivatives was assessed by the chromosome aberration assay. Our results show that ZEN as well as alpha- and beta-ZOL increased the percentage of chromosome aberrations in mouse bone-marrow cells and in HeLa cells. In the two systems, ZEN and alpha-ZOL exhibited the same range of genotoxicity and both were more genotoxic than beta-ZOL Furthermore, our results show that either ZEN or its two metabolites inhibited cell viability in a dose-dependent manner. We conclude that biotransformation of ZEN may be considered as only a partial detoxification pathway since the resulting metabolites remain relatively toxic. (C) 2011 Elsevier B.V. All rights reserved.