Branched chain amino acids (BCAA) improve nitrogen balance and end-organ function in surgical patients, but are untested in marrow transplant recipients. We compared nitrogen balance, urinary 3-methylhistidine-to-creatinine ratio, upper arm anthropometry, serum prealbumin, and day to peripheral engraftment in a randomized, double-blinded trial between 45% (high-leucine) and 23% BCAA intravenous solutions in 40 adult leukemia patients for 1 month following allogeneic marrow transplantation. Nutritional support, provided at approximately 30 nonprotein calories/kg and 0.21 g nitrogen/kg ideal weight, did not differ between groups. Despite