Compositions of matter comprising macromolecular hemoglobin

A composition of matter comprising a macromolecular hemoglobin capable of reversibly binding a gaseous ligand and selected from the group consisting of intermolecularly cross-linked, stromal-free deoxyhemoglobin and intermolecularly cross-linked, stromal-free oxyhemoglobin which macromolecular hemoglobin is intermoleculary cross-linked with a covalent cross-linking member having at least two cross-linking groups and selected from the members consisting of heterocyclic triazines, bis(diazobenzidines), halogenated aromatics, cycloalkanes, dialdehydes, sulfones, diisocyanates and diepoxides, and wherein the macromolecular hemoglobin is mixed with an acceptable carrier to form the composition useful as a blood substitute and as a plasma expander.