Respiratory failure secondary to acute lung inflammation is associated with quantitative and qualitative abnormalities of pulmonary surfactant. The surfactant-associated proteins (SP)-A, -B, and -C are critical for normal surfactant function, synthesis, and metabolism. Tumor necrosis factor-alpha (TNF-alpha), a primary mediator of acute lung inflammation, decreased SP gene expression in vitro (32, 34). In the present in vivo study, transient T cell activation and TNF-alpha release were initiated by intraperitoneal administration of anti-CD3 antibody 145-2C11. Serum TNF-alpha was elevated 2 h after injection of the antibody. SP-B and -C mRNA were decreased 12 and 24 h after antibody treatment. Intratracheal murine TNF-alpha also resulted in decreased SP-B and SP-C mRNA levels in the bronchiolar and alveolar epithelium of adult FVB/N mice, as demonstrated by S1 nuclease protection and in situ hybridization assays, despite minimal histological inflammation. SP-A mRNA was not significantly altered after anti-CD3 antibody and was only mildly decreased after TNF-alpha. As previously reported, intercellular adhesion molecule-1 mRNA was elevated after intratracheal TNF-alpha. SP insufficiency contributes to the pathogenesis of pulmonary diseases associated with increased TNF-alpha, such as adult respiratory distress syndrome and pneumonia (8). TNF-alpha-mediated decrease in SP gene expression may contribute to the surfactant dysfunction and atelectasis observed in inflammatory lung diseases.