A study was carried out to determine the oxyhemoglobin dissociation curve of stroma-free hemoglobin solution and factors which influence it, (pH; 2,3 DPG). 2) To simulate acute volume replacement, dilution experiments, in vitro, were performed employing both hemoglobin solution and Ringer's lactate in whole blood. 3) It was determined that stroma-free hemoglobin solution has a left-shifted oxyhemoglobin dissociation curve which responds to pH change but not to the addition of 2,3 DPG. 4) The dilutional effect of hemoglobin solution when mixed with whole blood in volumes up to 50% was to left-shift the oxyhemoglobin curve, unlike the effect of Ringer's lactate (no change). 5) This may have importance in the hemodynamic compensatory response to acute normovolemic anemia.