In acute liver failure (ALF), detoxification capacity of liver cells is reduced and a variety of cytokines, immune modulators, and toxic substances are accumulating. Multiple organ failure in ALF has been associated with increased blood cytokine levels. We have used a blood purification system, molecular adsorbent recirculating system (MARS), which is based on removal of both protein bound and water-soluble substances and toxins in liver failure. In this study, we measured the effect of MARS therapy on plasma cytokine levels in 49 patients with ALF. Interleukin 6 (IL-6), IL-8, IL-10 and tumor necrosis factor (TNF)alfa were determined immediately before and after the first MARS therapy and after the last session using enzyme-linked immunosorbent assays. The overall survival of these ALF patients was 82% at 6 months; the native liver recovered in 26 cases, and 14 were successfully transplanted. All three interleukins were increased before the MARS treatment but only anti-inflammatory IL-10 was reduced significantly during therapy, which in this setting could be interpreted as a positive effect. We were not able to show constant decreases in proinflammatory cytokines, but only transient effects on IL-8 and IL-6. Surprisingly TNFalfa level was normal and did not change during therapy. In theory, MARS albumin dialysis may remove toxic substances from the blood circulation and thereby improve the possibilities of the liver to recover; however, of the measured cytokines only IL-10 decreased significantly.