Drinking water contains disinfection byproducts, generated by the interaction of chlorine (or other disinfecting chemicals) with organic matter, anthropogenic contaminants, and bromide/iodide naturally present in most source waters. One class of these chemicals is the halogenated acetaldehydes (HAs), identified in high quantities when ozone is used as primary or secondary disinfectant. In this study, an analysis of the genotoxic potential of two HAs, namely tribromoacetaldehyde (TBA) and chloral hydrate (CH) has been conducted in human cells (TK6 cultured cells and peripheral blood lymphocytes). The comet assay was used to 1) measure the induction of single and double-strand DNA breaks, 2) evaluate the capacity of inducing oxidative DNA damage, and 3) determine the DNA repair kinetics of the induced primary genetic damage. In addition, chromosome damage, as a measure of fixed damage, was evaluated by means of the micronucleus test. The results of the comet assay show that both compounds are clearly genotoxic, inducing high levels of DNA breaks, TBA being more effective than CH. According to the comet results, both HAs produce high levels of oxidized bases, and the induced DNA damage is rapidly repaired over time. Contrarily, the results obtained in the micronucleus test, which measures the capacity of genotoxic agents to induce clastogenic and aneugenic effects, are negative for the two HAs tested, either using TK6 cells or human peripheral blood lymphocytes. This would indicate that the primary damage induced by the two HAs is not fixed as chromosome damage, possibly due to an efficient repair or the death of damaged cells, which is an important point in terms of risk assessment of DBPs exposure. © 2010.