The nutritional status of eight allogeneic bone marrow recipients was regularly evaluated for 3 months. All patients received supplemental total parenteral nutrition (TPN) in the acute posttransplant period. The study participants fell into two groups on the basis of their initial nutritional status, their clinical course, and progressive changes in their nutritional parameters. Although all patients experienced alterations in nutritional state; the four patients in Group I maintained more normal levels, while the four patients in Group II experienced greater declines and many complications leading to extended hospitalization or death. Nutritional influences unique to the bone marrow transplant process, but similar in effect to other intensive therapies for cancer, appeared to affect the reliability of the study parameters. Although influenced by the therapy, body weight, arm muscle circumference, triceps skinfold, creatinine-to-height index, and nitrogen balance did indicate an overall nutritional composite. Total parenteral nutrition, in the amount given, appeared to have positive but varying effect on all patients, although it was unable to prevent the observed declines in nutritional status.