Arsenic, a highly hazardous contaminant in our drinking water, accounts for various toxic effects (including cancer) in human. However, intake of arsenic @0.3μgkg(-1)day(-1) through drinking water, containing arsenic at its guideline value or maximum contaminant limit (10μgL(-1)), has been estimated to pose very little or no measurable risk to cancer in humans. The value also appears to be equal to the human reference dose (or index dose) of arsenic based on human skin toxicity data. The present work was a quantitative assessment of the genotoxic potential of arsenic in mice at doses equivalent to its human reference dose as well as its multiples. Significant increases in the frequencies of chromosome abnormalities in the bone marrow cells were registered over the control level upon exposure to all the doses of arsenic including its reference dose (or index dose). The assessment of arsenic genotoxicity in humans at low doses will therefore be highly instrumental in establishing a permissible limit of arsenic in drinking water.