Two oral administrations of 1,2-dibromoethane to adult female rats at doses above 10 micromoles/kg (1.9 mg/kg) caused DNA damage as determined by the alkaline elution technique. Far greater doses (300 micromoles/kg, 56.4 mg/kg) of 1,2-dibromoethane were required to cause other hepatic biochemical effects, such as increased activity of ornithine decarboxylase. In the dose range of 10-300 micromoles/kg, no increase in the activity of serum enzyme alanine transaminase (SGPT) was observed. Of the six organs studied, liver showed the largest amount of DNA damage. Thus, the carcinogen 1,2-dibromoethane caused substantial DNA damage at doses far below those required to show other biochemical effects or frank liver toxicity.