In rats, the administration of oil submitted to high temperatures is teratogenic. To understand the mechanisms involved, the clastogenic and cytotoxic effects were studied respectively in lymphocytes, hepatocytes (HepG2) and in human umbilical vein endothelial cells (HUVEC) cultured with a water extract obtained from heated oil (HO). In lymphocytes incubated with HO containing 0.075 or 0.15 microM of thiobarbituric reacting substances, the rate of chromosomal breakage was 18.4% and 23.1%, compared to 8.7% and 6.6%, or 8.1% and 9.2%, respectively in lymphocytes incubated with the same volume of a water extract from non-heated oil (NHO) or distilled water (DW). In HepG2 or HUVEC cells, the cytotoxic properties of the HO were dose dependent, the cytotoxicity beginning at concentrations as low as 0.25 microM. In contrast, the same volume of NHO or DW was non-toxic for these cells. The results obtained show that a water extract obtained from heated oil is clastogenic and, in higher doses, cytotoxic.