A critical feature of sepsis-induced adult respiratory distress syndrome (ARDS) is the release of cytokines (such as interleukin [IL]-6. IL-8, and tumor necrosis factor [TNF]) from endotoxin (lipopolysaccharide [LPS])-activated alveolar macrophages (AM). Nuclear factor kappa B (NF-κB) is activated in AM from patients with ARDS, and it is essential for the transcription of many cytokine genes. In these studies, we evaluated the regulation of LPS-induced cytokine release and the activation of NF-κB in human AM. We found that the activation of NF-κB and the release of IL-6, IL-8, and TNF from AM exposed to LPS was protein kinase C-independent and tyrosine kinase- and phosphatidylcholine-specific phospholipase C-dependent. We also found that LPS-induced activation of NF-κB was enhanced in AM cultured in serum or in the presence of LPS-binding protein, simulating conditions in the lung that are present in ARDS. In addition, LPS triggered the activation of several different NF-κB complexes in AM, and different forms of NF-κB bound to the IL-6, IL-8, and TNF promoter sequences. These observations suggest that physiologic abnormalities present in the lungs of patients with ARDS facilitate the activation of NF-κB and local release of cytokines.