BACKGROUND & AIMS During severe pancreatitis, interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha are produced in large quantities. The aim of this study was to determine whether either one plays a more dominant role and if their detrimental effects are additive. METHODS Necrotizing pancreatitis was induced in transgenic (-/-) knockout mice deficient in either IL-1 type 1 receptors, TNF type 1 receptors, or both IL-1 and TNF type 1 receptors. Wild-type mice served as controls. Mortality was assessed for 10 days. Additional animals were killed on days 0, 1, 2, 3, and 4 for determination of pancreatitis severity. RESULTS All three knockout groups showed decreased amylase and lipase, histological score, serum IL-6, and mortality compared with wild-type groups. Animals devoid of receptors for both cytokines showed improved survival and decreased IL-6 levels compared with those devoid of either IL-1 or TNF receptors individually, yet they failed to show a further decrease in pancreatitis severity. CONCLUSIONS Preventing the activity of IL-1beta or TNF-alpha has a nearly identical beneficial effect on the severity and mortality of acute pancreatitis. Preventing the activity of both cytokines concurrently has no additional effect on pancreatitis severity but further attenuates the systemic stress response and is associated with an additional but modest decrease in mortality.