One of our major aims was to find ways to utilize outdated or virus-contaminated blood. Pyridoxylated hemoglobin (PLP-Hb), a possible substitute for red cells as an artificial oxygen carrier was prepared from outdated human blood. By conjugation with polyethylene glycol (PEG), the biological half life was increased about 3 folds at 82% blood replacement in rats without significant side effects in vivo or in vitro. We next tried to prepare virus-free PEG-PLP-Hb from HBV or HTLV-I positive blood. A considerable amount of HBV (Dane particles) could be removed from HBV-positive red cells by washing and during the preparation of PEG-PLP-Hb. When the hemoglobin preparations containing Dane particles were filtered through a porous cellulose filter, BMM-30 (30 nm pore size, Asahi Chemical Industry Co., Ltd., Osaka, Japan), HBV-DNA in the filtered fractions became less than 0.33% of the initial amount. More than 96% of blood leukocytes could be removed with a leukocyte removal filter, Sepacell R-500 (Asahi Medical Co., Ltd., Tokyo, Japan). The leukocytes collected from filtrated fractions of HTLV-I positive blood did not survive beyond 3 days. Since transmission of HTLV-I occurs by cell to cell contact and is rare in cell-Free condition, it is unlikely that the PLP-Hb prepared from HTLV-I positive blood which is deprived of leukocytes transmits HTLV-I infection.