The optimal mode of clearance in critically ill patients with acute kidney injury (AKI) who require renal replacement therapy (RRT) is unclear. Although both convection (as provided by hemofiltration) and diffusion (as provided by hemodialysis) provide equivalent removal of small-sized molecules, hemofiltration offers the potential for removal of large molecules many of which may be toxic. Hemofiltration and hemodialysis have never been compared in a rigorous randomized trial to date.