Background: To assess the effects of treatment with nebulized corticosteroids immediately after chlorine gas injury, Methods: Eighteen anesthetized and mechanically ventilated pigs were exposed to chlorine gas (140 ppm for 10 minutes) and observed for 6 hours. Nine pigs were treated with nebulized beclomethasone-dipropionate 20 mu g/kg (BDP group), and nine pigs were given no treatment (control group). Results: All animals developed severe pulmonary dysfunction, The initial decrease in Pao(2) was similar in both groups, but BDP-treated animals improved whereas control animals deteriorated (p < 0.005; analysis of variance). Pulmonary vascular resistance increased in both groups but less in the BDP group (p < 0.01). Lung-thorax compliance was better preserved in the BDP group (p < 0.01), and oxygen delivery was significantly better in the BDP group (p < 0.01), One animal died in the BDP group, as did three animals in the control group. Conclusion: Immediate treatment with nebulized BDP improved pulmonary and cardiovascular function after experimental chlorine gas injury.