Lipopolysaccharides (LPS) released from Gram-negative bacteria after infection initiate an exagerated response that leads to a cascade of pathophysiological events termed sepsis. Monocytes or macrophages produce many of the mediators found in septic patients. Targeting of these mediators, especially tumor necrosis factor (TNF)-alpha and nitric oxide (NO), has been pursued as a mean of reducing mortality in sepsis. Bovine dialyzable leukocyte extract (bDLE) is a dialysate of a heterogeneous mixture of low-molecular-weight substances released from disintegrated leukocytes of the blood or tissue lymphoid. In this study, to determine whether bDLE modulates NO and pro-inflammatory cytokine production, murine peritoneal macrophages were treated with bDLE (0.05 or 0.5 U/mL) before LPS (20 mg/mL) stimulation, and also LPS-stimulated murine peritoneal macrophages were treated with bDLE (0.05 or 0.5 U/mL) at 0, 4, 8, 12, and 24 hours. The bDLE significantly decreased NO production, and also decreased TNF-alpha and interleukin (IL)-6 but increased IL-10 production in LPS-stimulated murine peritoneal macrophages. Our results demonstrate that bDLE plays an important role in modulating TNF-alpha, IL-6, and NO production through IL-10, and this may offer therapeutic potential in clinical endotoxic shock.