Induction of oxidative stress by 2,4-dichlorophenoxyacetic acid (2,4-D) both as a pure compound and in commercial formulation was investigated during early pregnancy in mice. Pregnant animals were exposed to increasing doses of the herbicide (0.01, 0.1 and 100mg/kg/d) during gestation days 0-9, after which animals were euthanized and their blood analyzed for catalase activity, thiobarbituric acid reactive substances (TBARs) and total antioxidant capacity (TAC). Number of corpora lutea and uterine implantations and resorptions were also determined. Herbicide exposure did not cause any overt signs of maternal toxicity at any of the doses administered; neither did it cause an effect on developmental parameters. Catalase activity and TBARs were not modified by herbicide exposure although TAC was significantly decreased at 100mg/kg/d of both pure and formulated compound. Thus, 2,4-D does not seem to induce oxidative stress during early pregnancy in mice at the doses administered, indicating that this mechanism is probably not involved in mediating herbicide toxicity at these dose levels. Furthermore, since no manifestations of developmental toxicity were observed after administration of the herbicide, it is also possible that 2,4-D may not produce any early developmental toxicity at the low environmentally relevant doses tested in this animal model.