Human hemoglobin was pyridoxalated and subsequently coupled with the activated ester of polyethylene glycol (PEG) to provide an oxygen-carrying resuscitation fluid. The PEG conjugate of pyridoxalated hemoglobin (pyridoxalated PEG hemoglobin) has a longer half-life in the circulation (12.8 h) than does hemoglobin (2.2 h) when the solutions are exchange-transfused by approximately 60%. The P50 of pyridoxalated PEG hemoglobin, which is the partial pressure of oxygen at which one-half of the absorbed oxygen is released, was 21.3 +/- 1.4 mm Hg (mean +/- SD, n = 5) (37 degrees C, pH = 7.4), which is close to that of human whole blood (25.9 +/- 0.6 mm Hg). The colloidal osmotic pressure and the viscosity were 36.5 +/- 2.4 mm Hg (n = 5) and 2.6 +/- 0.4 cp (n = 5), respectively. The results indicate that the pyridoxalated PEG hemoglobin solution has favorable properties for use as an oxygen-carrying resuscitation fluid.