To determine if an enhancement in the fetal antioxidant enzyme (AOE) system by maternal dexamethasone (DEX) is specific to organ and dose, the lung and kidney of pups, whose mother received DEX (0.2 or 2 mg/kg) twice, were obtained on days 19 and 20 of gestation. Low-dose DEX increased the four AOE in the day-19 lung, but not in day-20 lung. High-dose DEX decreased the copper-zinc superoxide dismutase (SOD) and glutathione peroxidase in the lungs. Thus, the DEX-induced maturation of lung AOE is dependent on dose and timing. DEX enhanced the four AOE in the day-19 kidney at both doses. In the day-20 kidney, DEX enhanced the manganese SOD at the low dose and also catalase at the high dose, suggesting that DEX accelerates the maturation of kidney AOE as well.