In the present study, DNA damaging and mutagenic effects of chlorinated drinking water (CDW) extracts obtained from polluted raw water resources were examined in metabolically competent human Hep G2 hepatoma cells using the in vitro micronucleus assay and the single cell gel electrophoresis (SCGE, comet assay). Additionally, the in vivo induction of micronuclei (MN) was studied in polychromatic erythrocytes (PCEs) derived from bone marrow of CDW-treated Wistar rats. Furthermore, we examined the influence of CDW on the lipid peroxidation (LpO) in blood, liver, kidney and testicle of rats. The results demonstrated significant increases of micronucleated PCEs in the bone marrow of rats fed with relatively low CDW doses (33.3ml/kg body weight per day). Similar effects, i.e. increases of MN frequencies, were found in Hep G2 hepatoma cells after CDW treatment (41 MN/1000 binucleated cells (BNCs) for 167ml CDW) in comparison to the vehicle control (24 MN/1000 BNC). Additionally, DNA damages caused by CDW were observed in the comet assay. As a product of LpO, the levels of malondialdehyde (MDA) were significantly enhanced almost in all animals and organs tested after CDW treatment. In livers and serum of rats dose-dependent increases of MDA were observed. The data indicated that extracts from CDW obtained from polluted raw water were able to cause oxidative damages and to induce various biological effects in mammalian cells in vivo and in vitro, i.e. clastogenicity and/or aneugenicity, DNA strand breaks and/or alkali-labile damages. The consistency of the results among the various biological systems and endpoints led to the conclusion that the consumption of chlorinated drinking water obtained from polluted raw water may enhance the body burden with mutagenic and/or carcinogenic substances and therefore, means a potential genetic hazard for human health.