Following aspiration of 0.1N hydrochloric acid with pH 1.0, 20 mongrel dogs were ventilated mechanically for four hours. Positive end-expiratory pressure of 10 cm H2O was added continuous positive-pressure ventilation (CPPV). In addition to CPPV, ten of the dogs received methylprednisolone (30 mg/kg body weight). The CPPV improved arterial oxygen tension, decreased venous admixture, increased arterial-venous oxygen content difference, and decreased systemic blood pressure. The addition of methyl-prednisolone did not significantly improve oxygenation, survival, or any other variable measured.