Veno-occlusive disease (VOD) of the liver is a significant complication for some patients undergoing hematopoietic stem cell transplantation. This disease is thought to be a toxicity secondary to chemotherapy or radiation-induced damage to the epithelial cells of the blood vessels in the liver. VOD is categorized as mild, moderate or severe. Historically, there has been no method to treat the disease. Recently, however, there have been investigations into the use of a new agent called defibrotide.