A comparison was made of van't Hoff i values calculated from hemolytic and freezing point data for various salts of gluconic acid. Sodium, potassium, and maoganese (II) gluconates gave higher i values by the hemolytic method than by the freezing point depression method; iron(II) and cobalt(II) gluconates gave lower i values by the hemolytic method. Magnesium and calcium gluconates gave higher i values by the hemolytic method with human erythrocytes but not with rabbit erythrocytes. Zinc gluconate gave extremely high hemolytic i values due to the partial precipitation of the oxyhemoglobin liberated from laked erythrocytes. Hemolytic i values of the gluconates were generally lowered when determine in the presence of sodium chloride. Erythrocytes from Negro donors were, on the average, more resistant to osmotic hemolysis than those from Caucasian donors. Results substantiate the premise that solutions calculated to be iscomotic with blood according to colligative property data are not necessarily isotomic to the red corpuscle.