Hemodialysis is a lifesaving procedure for patients with acute renal failure. Nevertheless, the institution of hemodialysis may result in a continued or accelerated decline in renal function. Loss of osmotic drive and hypotension may be partially responsible for this observation. However, multiple lines of evidence suggest that the nature of the hemodialysis membrane also influences renal function following acute renal failure. The cellulosic hemodialysis membrane activates humoral pathways and the cellular elements of blood. The inflammatory responses entrained from the activation result in hypersensitivity reactions attributable to anaphylatoxin generation, hypoxemia, increased susceptibility to infection, and catabolic events. In addition, recent studies indicate that the use of bioincompatible membranes delays recovery from acute renal failure. Increased numbers of neutrophils are found in the glomeruli following exposure to cellulosic membranes, suggesting that inflammatory events induced by complement activation may mediate continuing renal injury and prolonged recovery from acute renal failure. Membrane choice for patients with acute renal failure is emerging as an important therapeutic consideration, just as it is for those patients on long-term dialysis.