ABSTRACT. The effect of dexamethasone (0.1, 1, and 5 mg/kg/d given subcutaneously from d 14-18) was tested in infant mice continuously exposed from birth to either humidified air or 80% oxygen. Dexamethasone significantly decreased lung wet wt ( p < 0.01), lung water ( p < 0.021), lung dry wt, protein, and DNA ( p < 0.001) in both airand oxygen-exposed animals. Dexamethasone, however, had no effect on lung compliance measured after animals were killed on d 18. It also had no effect on the increase in the blood-air barrier thickness or decrease in the blood-air exchange surface area seen in the 80% oxygen-exposed mice. Dexamethasone decreased thymus gland wt ( p < 0.001), body wt gain ( p < 0.001), brain wt ( p < 0.001), and lung lymphocytes ( p < 0.05) in both air-and oxygen-

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