The objective of this study was to evaluate the relation between the clinical and plasma parameters and the changes in plasma endotoxin activity with 2 hours of endotoxin-adsorbing therapy using polymyxin B (PMX). A total of 88 consecutive patients were admitted for PMX treatment of severe sepsis or septic organ failure. Standard supportive care was continued without alteration during PMX treatment. Endotoxin, tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6), IL-10, and plasminogen activator inhibitor-1 (PAI-1) activities and clinical parameters were measured before, immediately after, and the day after PMX treatment. The mean APACHE II and III scores were 24.2 +/- 1.0 and 85.8 +/- 3.0, respectively. The 2-week survival rate was 51.1%. In survivors, TNFalpha, IL-6, IL-10, and PAI-1 activities were significantly decreased during the 2-hour PMX treatment, the following day, or both times. There was no significant change in the parameters, except for TNFalpha, after PMX in nonsurvivors. In the subgroup whose plasma endotoxin decreased more than 30%, IL-6, TNFalpha, and PAI-1 significantly decreased after 2 hours of PMX or the following day (or both), but all four parameters in nonsurvivors showed no significant change. Hence PMX adsorbed plasma endotoxins and contributed to reductions in plasma proinflammatory cytokine levels and to improved clinical parameters during the 2-hour treatment. Changes in these parameters correlated with changes in plasma endotoxin activity in survivors whose plasma endotoxin levels were adequately reduced.