Abstract: Hemoglobin preparation suited for intravenous injection with increased oxygen release in relation to erythrocytes or hemoglobin solution, comprising a substantially pyrogen-free condensation product of hemoglobin and pyridoxal phosphate having a retention time in the blood vessel from about 2 to 9 hours. It is produced by washing human erythrocytes at least four times with a weakly alkaline solution, then hemolyzing and treating the material with a cation exchange resin in the H+ form until the pH value has dropped to about 5 to 5.5, separating the material from resin and any precipitated stroma, diluting the material to a hemoglobin concentration of about 5 to 9%, adjusting the pH to about 7 to 9, displacing any oxygen therein, and adding about 0.25 to 1.25 g of pyridoxal-5-phosphate per liter of hemoglobin solution of 5 to 9% concentration.