The validity of biochemical indices routinely used for nutritional assessment was evaluated in patients undergoing allogeneic bone marrow transplantation for hematologic malignancies. Sixteen patients received total parenteral nutrition (TPN) for 15 days (35 kcal kg.body wt-1.day-1; 1.4 g amino acid.kg body wt-1.day-1) starting 1 day after transplantation. Nutritional status was evaluated before and after the TPN period by determining anthropometric (body weight, triceps skinfold thickness, and midarm circumference) and biochemical (transferrin, prealbumin, ceruloplasmin, and C3c) indices. Anthropometric indices, which were within the normal range before TPN, were not changed on day 15; transferrin and prealbumin concentrations significantly (p = 0.03) decreased whereas ceruloplasmin and C3c significantly (p = 0.03) increased. The levels of acute-phase proteins (alpha-1-acid glycoprotein, alpha-1-antitrypsin, and C-reactive protein), determined in 8 of the 16 patients at the same time intervals, were increased after 15 days of TPN and were significantly inversely correlated with transferrin and prealbumin. On the basis of these data, it appears that biochemical indices are not sufficiently reliable in the nutritional assessment of bone marrow transplantation patients because the levels of these substances are markedly affected by the acute-phase response secondary to febrile episodes and graft-versus-host disease, which frequently complicate transplantation.