Abstract 1. 1. Following occlusion of the circulation to the eye of bluefish a ferric hemeprotein (or proteins) appears in the blood plasma of the ophthalmic blood vessels. 2. 2. This protein may play a role in the establishment of elevated oxygen pressures by the choroid rete mirabile. 3. 3. A hemeprotein (or proteins) is occasionally found in the systemic blood plasma of Amia calva. It combines reversibly with oxygen and with carbon monoxide. Ligand binding is co-operative, suggesting that the protein has two or more interacting subunits. 4. 4. Ferrous bluefish and Amia hemeproteins exhibit hemochromogen spectra, indicating that the distal ligand position of the heme is occupied by a nitrogenous (or sulfurous) ligand.