A decreased risk for lung cancer after exposure to cotton dust has been demonstrated in epidemiological and experimental investigations. To study possible cellular mechanisms, animals were exposed to airborne endotoxin and the production of tumor necrosis factor (TNF) and Interleukin-1 (IL-1) was measured in alveolar macrophages obtained by airway lavage. The endotoxin exposure induced a significant increase in TNF and IL-1 production at two hours after exposure. A renewed exposure of the cells to endotoxin in vitro further augmented the production of IL-1.