When hospital-acquired acute renal failure (ARF) is severe enough to require renal replacement therapy, mortality rates are extremely high, exceeding 50%. The potential impact of renal replacement therapy on clinical outcomes in ARF remains a subject of ongoing investigation and controversy. This article reviews in depth all of the clinical trials that have examined the effect of dialysis-related variables on clinical outcomes in patients with ARF requiring intermittent hemodialysis. In particular, the role of biocompatibility of dialyzer membranes, and timing, intensity, and adequacy of dialysis are discussed.