In patients with septic shock and multiorgan failure including acute renal failure, the prognosis is poor. This study evaluated the effects of plasma exchange as adjunctive therapy to the conventional treatment in such severely ill patients and compared the results with the expected outcome according to data from other studies. A total of 25 patients (17 men and 8 women, mean age 47, range 15-74 years) were treated by a median of 3 (range 1-10) plasma exchanges, mainly by centrifugation technique. The main replacement fluid was liquid-stored plasma and albumin (in a few cases fresh frozen plasma). About 80% of the patients also received low doses of steroids (hydrocortisone 200-400 mg/day and heparin 1,000-25,000 U/day). Twenty of the patients survived (80%) which was significantly better than was expected by conventional treatment (< 20% survival, p < 0.001). The relative chance to survive was four times greater than expected. Five patients died. The reason of death was cerebral hemorrhagia, brain abscess, myocardial sudden death, relapsing sepsis from multiple hepatic abscesses, and a psoas abscess which was not drained. The patients who survived regained almost total renal function and could leave the hospital with only a few sequelae. The plasma exchange may be a good adjunct to conventional therapy to increase the chance of survival when other treatment is insufficient. The mechanisms by which plasma exchange acts may be by removal of endotoxins derived from microorganisms or tissue necrosis and removal of excessive amounts of cytokines together with a modification of various cascade systems enabled by the products in the plasma from the healthy donors, used for replacement.