Bone marrow transplantation (BMT) is associated with severe metabolic stress secondary to anorexia, mucositis, enteritis, and infection. We compared nutritional parameters and clinical outcomes of 22 patients who received prophylactic total parenteral nutrition (TPN) to those of 22 controls, matched for age and diagnosis, who received nutritional supportad libitum.Over the 5-week study period, the TPN group averaged caloric intakes greater than 1.5 × basal energy expediture (BEE) per day and gained 2.5% of body weight; the control group averaged less than 0.9 × BEE and lost 3.7% of body weight. Visceral protein status as reflected by serum albumin was not different. Engraftment of donor marrow cells was 3 days earlier (p < 0.01) in the TPN group than in the controls, despite there being no significant difference in the number of marrow cells each group received. There was no difference in the two groups' clinical outcomes; mortality, duration of hospital stay, and incidences of sepsis, graft-versus-host disease, and return of malignancy were equivalent. Thus, patients who received prophylactic TPN engrafted sooner than patients who did not; however, overall clinical outcome was unaffected by TPN. Controlled studies of prophylactic TPN are indicated for the BMT patient population.