Two adolescents who underwent successful allogeneic bone marrow transplantation were nutritionally managed on a fat-free cyclic parenteral nutrition (PN) regimen. Serum concentrations of prealbumin, albumin, and transferrin were prospectively evaluated to assess the efficacy of nutritional therapy. Both patients tolerated the cyclic PN metabolically. Serial albumin and transferrin concentrations varied slightly and were less sensitive indices of changing nutritional status. In contrast, prealbumin concentrations decreased uniformly during periods of metabolic stress. At the cessation of Pn therapy, all serum proteins were within the normal range. Cyclic PN appears to be a safe, practical approach to the nutritional management of patients undergoing bone marrow transplantation.