The aim of this research was to evaluate the potential genotoxic effects of three drinking water disinfectants by means of in vivo short-term mutagenicity tests using plants. The study was carried out in laboratory using distilled water disinfected with sodium hypochlorite (NaClO), chlorine dioxide (ClO2) and peracetic acid (PAA) at different concentrations both in neutral and acid conditions. Untreated distilled water was used as a negative control. Micronuclei test in Tradescantia pollen cells and chromosomal aberration test in root cells of Allium cepa were the bioassays performed by exposing directly plant bioindicators to treated and untreated distilled water. The Tradescantia/micronuclei test gave positive results in most of the ClO2-treated water samples but only at acid pH. The Allium cepa test showed genotoxicity in NaClO-treated samples at acid pH and in a ClO2-treated sample at pH 7. PAA-treated samples were always nongenotoxic. Since the concentrations tested of free disinfectants are usually present in drinking water for biocidal purposes, genotoxicity of these compounds could be a public health problem.