Disinfection by-products (DBPs) are chemicals that are produced as a result of chlorine being added to water for disinfection. As well as the halogenated DBPs, N-nitrosamines have recently been identified as DBPs, especially when amines and ammonia ions are present in raw water. In this work, the genotoxicity of two nitrosamines, namely nitrosodimethylamine (NDMA) and nitrosodiethylamine (NDEA), has been studied in cultured human cells. To evaluate their genotoxic potential two assays were used, the comet assay and the micronucleus test. The comet assay measures the induction of single and double-strand breaks, and also reveals the induced oxidative DNA damage by using endolll and FPG enzymes. Chromosomal damage was evaluated by means of the cytokinesis-blocked micronucleus test. The results of the comet assay show that both compounds are slightly genotoxic but only at high concentrations. NDEA being more effective than NDMA. Enzyme treatments revealed that only NDEA was able to produce increased levels of oxidized bases, mainly in purine sites. The results obtained in the micronucleus assay, which measures the capacity of the tested agents to induce clastogenic and/or aneugenic effects, are negative for both of the nitrosamines evaluated, either using TK6 cells or human peripheral blood lymphocytes. Taking into account the very high concentrations needed to produce DNA damage, our data suggest a low, if existent, genotoxic risk associated with the presence of these compounds in drinking water. (C) 2010 Elsevier B.V. All rights reserved.