The epigenetic and genotoxic action of ethylene glycol monobutyl ether (2-butoxyethanol) has been studied in rats and transgenic mice. In rats we have administered per os one acute dose (1 mmol/kg) and the animals were killed 24 h later. In the case of transgenic mice (carrying the v-Ha-ras oncogene controlled by the Mouse Mammary Tumor Virus promoter) 10 mmol/kg were administered over 2 weeks using subcutaneously implanted osmotic minipumps. The latter animals were terminated 5, 10, 15, 60, 90 and 120 days after 120 days after the first day of administration. The effect of 2-butoxyethanol was examined at the DNA level of 5 organs : liver, brain, kidney, spleen and testis using 32P postlabelling methods. We have thus investigated the possible formation of hydrophobic adducts and the 5-methyldeoxycytosine content in the DNA of rats and transgenic mice. Moreover, the methylation of the ras genes as well as the tumor formation in mice were assessed. Neither hydrophobic nor hydrophilic adducts were detected in the DNA of treated rodents compared to controls. Concerning the level of 5-methyldeoxycytosine found in the DNA of chemically treated rats as compared to control one, no differences could be detected. In addition the study of the methylation at the ras genes did not show significant differences between control and treated animals. At necropsy there was no statistical difference in the tumor formation between control and 2-butoxyethanol did not display epigenetic and genotoxic effects in neither rats nor initiated transgenic mice carrying v-Ha-ras oncogene.