We, the researchers at Vanderbilt University, propose to perform a randomized, prospective, double-blind, placebo-controlled study of 144 patients undergoing allogeneic marrow transplantation. The treatment is aimed at supporting hepatic urea cycle function in patients receiving escalated dose chemotherapy/BMT. By so doing we hope to prevent development of hepatic venoocclusive disease (HVOD) and acute lung injury (ALI), two morbid complications of BMT. Patients will be randomized to receive oral citrulline, a urea cycle amino acid intermediate, or placebo beginning before conditioning therapy and continuing until 21 days after BMT. All patients will be followed for 100 days after study enrollment with intensive data collection.