Organic acids activated by esterification with 3,5-dibromosalicylate react preferentially either with the beta 82 lysines or the alpha 99 lysines of hemoglobin. The versatility and site specificity of these polysapirins and the usage of both human and bovine hemoglobins allowed the construction of a family of oxygen carriers with various P50 ranging from 10 to 50 mmHg. These derivatives are obtained in pure homogeneous form by column chromatography. They are stabilized tetramers where the dissociation into dimers is inhibited. The latest addition is Tri-(3,5,dibromosalicyl)-benzenetricarboxylate, which crosslinks both human and bovine hemoglobin across the beta subunits, decreasing the oxygen affinity of both proteins. The crosslinked hemoglobins have a normal Bohr effect, more expanded in the alkaline region, and are sensitive to chlorides but not to polyphosphates. Solutions of stabilized tetramers, infused into rats or cats up to 25-50% blood replacement, do not produce altered renal and cardiac function. In the cat isovolemic hemodilution increases cerebral flow in controls treated with albumin solutions, when an oxygen carrier is used the cerebral flow remains normal.