The blood from 19 patients having bone marrow transplantation was examined for the essential antioxidants alpha-tocopherol and beta-carotene as well as lipid hydroperoxides before, at and after bone marrow transplantation (BMT). Conditioning therapy, preceding BMT in order to achieve marrow ablation and immunosuppression, consists of high-dose chemotherapy which is mostly combined with total body irradiation (TBI). In order to see a possible difference between patients with and without additional TBI, we divided the patients up into two groups; patients receiving TBI (RT+) and patients without TBI (RT-). All patients required total parenteral nutrition beginning one week prior to BMT. After conditioning therapy plasma levels of absolute and lipid-standardized alpha-tocopherol and beta-carotene decreased in both groups, presumably as a result of an enhanced breakdown of these antioxidants. The loss of these lipid-soluble antioxidants has to be considered as a possible cause for early post-transplant toxicity. Lipid hydroperoxides increase significantly in the group of patients with additional TBI, whereas the other group, receiving no additional TBI, showed no significant change. We suggest high-dose supplementation of essential antioxidants for patients undergoing BMT.