The effectiveness of plasma exchange (PE) with continuous hemodiafiltration (CHDF) in the treatment of critically ill patients was evaluated based on changes in cytokine levels. Twenty-six patients with acute hepatic failure were treated with PE (PE group) or PE and CHDF (PE+CHDF group), and the levels of cytokines such as tumor necrosis factor (TNF)-␣, interleukin (IL)-6, and IL-8 were determined before and after treatment. Bilirubin levels were significantly lower after treatment in both the PE and PE+CHDF groups. There were no significant differences in TNF-␣ levels before and after treatment in the PE group, but the TNF-␣ level was significantly lower after treatment in the PE+CHDF group. There were no significant differences in the IL-6 levels before and after treatment in both the PE and PE+CHDF groups. There were no significant differences in IL-8 levels before and after treatment in the PE group, but the IL-8 level was significantly lower after treatment in the PE+CHDF group. PE with CHDF therapy was given to 5 patients with acutely aggravated autoimmune diseases, 2 patients with hemorrhagic shock and encephalopathy syndrome, and 3 patients with thrombotic microangiopathy. The results suggested that PE with CHDF therapy are useful in critically ill patients with suspected hypercytokinemia.