To examine the relationship between arachidonic acid metabolism and sepsis, we determined the blood concentration of platelet-activating factor acetylhydrolase (PAFAH) and of arachidonic acid cascade substances, leukotriene B4 (LTB4), thromboxane B2 (TXB2), and 6-keto-prostaglandin Fla (PGFla), in patients with clinical sepsis. Blood concentrations of PAFAH, LTB4, TXB2 and PGFla at the time of the initial diagnosis of sepsis were 23.9+/-9.7 nmol/min/mL, 90.4+/-31.5 pg/mL, 55.3+/-44.1 pg/mL and 22.3+/-11.9 pg/mL, respectively. There was a significant correlation between the blood PAFAH and LTB4 concentration (r = 0.520, p = 0.0033) and the diagnosis of sepsis. There also was a significant correlation between the blood PAFAH and TXB2 concentration (r = 0.460, p = 0.0311). There was no correlation between the blood PAFAH and PGFla concentrations. Elevated LTB4 and TXB2 concentrations showed a significant correlation with the PAFAH concentration in patients with sepsis, suggesting a direct relationship between these substances.