In 32 patients with acute pancreatitis (AEP = 15, ANP = 17), tumor necrosis factor (TNF) activity, oxygen-derived free radicals (OFR) and endotoxin contents were determined by L929 cell bioassay, Tetrabarbituric acid fluorometry and Limulus test respectively. The results showed that TNF and OFR elevated in patients with AP at the admission (P < 0.05 vs normal). The change of TNF and OFR responded to the clinical symptoms. TNF correlated to early multiple organ failure (MOF). In patients with late MOF, TNF and OFR were both the important factors. By measuring endotoxin, we found that endotoxemiae were not so important in early phase of the disease as in late phase, in which they made TNF and OFR released profusely.