Acute pulmonary injury occurs frequently following hemorrhage and injury. In order to better examine the sequence of events leading to lung injury in this setting, we investigated lung histology as well as in vivo mRNA levels for cytokines with proinflammatory and immunoregulatory properties (IL-1 beta, IL-6, IL-10, TNF-alpha, TGF-beta, IFN-gamma) over the 3 days following hemorrhage and resuscitation. Significant increases in mRNA levels for IL-1 beta, IL-6, IL-10, and IFN-gamma, but not TNF-alpha, were present among intraparenchymal pulmonary mononuclear cells obtained 1 and 3 days after hemorrhage. Among alveolar macrophages, TNF-alpha and IL-1 beta mRNA levels were increased 3 days after hemorrhage. Few changes in cytokine mRNA levels, with the exception of TNF-alpha at 3 days after hemorrhage, were present among peripheral blood mononuclear cells. Histologic examination of lungs from hemorrhaged animals showed no alterations 1 day after hemorrhage, but neutrophil and mononuclear cell infiltrates, edema, intra-alveolar hemorrhage, and fibrin generation were present 3 days after hemorrhage. These results suggest that hemorrhage-induced enhancement of proinflammatory cytokine gene transcription may be an important mechanism contributing to the frequent development of acute lung injury following blood loss and injury.