The Fe Kß fluorescence emission spectrum was used to study the coordination of iron in some heme proteins. The spectrum was found to be dependent only on the direct environment of the iron. The iron atom in oxyhemoglobin can be regarded as trivalent, with a considerable negative charge on the outer oxygen atom of the O2 ligand. Carbonmonoxide hemoglobin contains divalent, zero spin iron. Methemoglobin is a low spin compound.