Background: Using different types of dialysis membranes to treat acute renal failure (ARF), clinical and experimental studies have demonstrated discordant results relatively to the effect of membrane bioincompatibility on patient outcome. Nevertheless, there are few data on the biocompatibility indices in patients with ARF who need to be treated by hemodialysis. Objective: To characterize the impact of intermittent hemodialysis (IHD) on indices of leukocyte, platelet and endothelial activation in patients with ARF. Patients and Methods: We prospectively studied 27 patients with severe ARF treated by IHD. They were characterized relatively to gender, age, ARF etiology, urinary output per 24 h, Simplified Acute Physiology Score (SAPS), number of dialysis sessions and outcome. We evaluated the effect of hemodialysis with two types of low-flux dialyzers (cuprophane and polysulfone dialyzers) on plasma concentrations of soluble TNF-RI (TNF-sR55), TNF-RII (TNF-sR75), interleukin (IL)-6, soluble CD23 molecule, soluble P-selectin and von Willebrand factor (vWF). Results: There were no significant differences between the two groups of patients dialyzed with cellulose-based and synthetic membranes in terms of age, sex, urinary output per 24 h, SAPS, number of dialysis sessions and mortality. We verified high plasma concentrations of TNF-sR55, TNF-sR75, IL-6, sCD23, sP-selectin and vWF in the global population studied. Patients dialyzed with cuprophane membranes showed significantly lower pre- and postdialysis concentrations of sP-selectin than patients dialyzed with polysulfone membranes. After a hemodialysis session, with correction for differences of blood hematocrit, we did not observe any significant modification in the concentrations of TNF-sR55, TNF-sR75, IL-6, sP-selectin and vWF of the plasma. On the other hand, a significant increase of sCD23 molecule was found in the group dialyzed with polysulfone membranes (p = 0.009). Conclusions: The group of 27 patients with ARF who needed IHD, showed increased plasma concentrations of some leukocyte, platelet and endothelial activation markers (TNF-sR55, TNF-sR75, IL-6, sCD23, sP-selectin and vWF). These mediators characterize the inflammatory and procoagulant state associated with this pathologic condition. After a hemodialysis session with these low-flux membranes (cellulose-based and polysulfone membranes), we did not observe any significant variation in the concentrations of TNF-sR55, TNF-sR75, IL-6, sP-selectin and vWF of the plasma. Patients dialyzed with polysulfone membranes presented higher basal plasma concentrations of sP-selectin and significant postdialysis increase of plasma concentrations of CD23 molecule compared to patients dialyzed with cuprophane dialyzers.