For children undergoing bone marrow transplantation, respiratory failure is a devastating complication, with mortality expectations well above 60%. The researchers have devised a novel strategy that may greatly improve survival. Hemofiltration, a continuous form of dialysis, was designed as a therapy for critically ill patients with kidney failure. A semi-permeable membrane removes plasma water and solutes (up to about 35,000 Daltons molecular weight). The researchers have treated immuno-compromised children with respiratory failure with hemofiltration. Many inflammatory molecules are of a size well below the limit of the filter. Hemofiltration might remove a critical amount of this inflammatory material, attenuating the unregulated inflammatory response that is central to the development of respiratory failure and progression to multiple organ failure and death. The researchers are conducting a multi-center trial of early continuous hemofiltration for respiratory failure in children following bone marrow transplantation. The researchers will analyze blood and ultrafiltrate using sensitive proteomic methods to detect several inflammatory biochemicals known to be active in this disease, looking for evidence that early active hemofiltration alters the inflammatory response. The researchers will test whether `early` hemofiltration produces greater survival from respiratory failure in this vulnerable population.