The aim of this study was to investigate the effects of combination therapy with melatonin and dexamethasone (DEX) on acute lung injury. In particular, we investigated the effects of combination therapy in animal models of acute lung inflammation (carrageenan-induced pleurisy). Injection of carrageenan into the pleural cavity of rats elicited an acute inflammatory response characterized by fluid accumulation in the pleural cavity which contained a large number of neutrophils [polymorphonuclear leukocyte (PMN)] as well as an infiltration of PMN in lung tissues and subsequent lipid peroxidation, and increased production of nitrite/nitrate (NOx), and prostaglandin E2 (PGE2). Furthermore, carrageenan induced an upregulation of the adhesion molecules ICAM-1 and P-selectin, inducible nitric oxide synthase, cycloxygenase-2 as well as nitrotyrosine as determined by immunohistochemical analysis of lung tissues. No anti-inflammatory effect was observed in animals treated with melatonin (10 mg/kg) or with DEX (0.01 mg/kg) alone. This study shows that the combination therapy with melatonin and DEX reduced the degree of acute lung inflammation and tissue damage associated with carrageenan-induced pleurisy in mice and supports the possible use of melatonin in combination with steroids in order to reduce the dose and the side effects related with the use of steroids for the management of inflammatory disease.