We have previously shown that administration of the antioxidant butylated hydroxytoluene (BHT) to mice produces lung damage that can be markedly potentiated by hyperoxia resulting in pulmonary fibrosis. In the present studies using this model, we show that: (1) in animals treated with BHT-O2, prednisolone given for 12 successive days does prevent excessive collagen accumulation provided lung collagen is measured immediately after terminating steroid therapy, whereas a rebound effect occurs later on; (2) limitation of steroid treatment to the first 6 days after acute lung injury enhances accumulation of collagen, whereas steroids given later, on Days 7 through 12, have an alleviating effect; (3) indomethacin under the conditions described is not an effective treatment.