The species specific muscle myogens ofSalmo gairdnerii,Oncorhynchus masou,O.masou ishikawae,O.kisutch,O.tshawytscha,O.keta,O.nerka, andO.gorbuschaare compared by starch gel electrophoresis. Plasma proteins of these same species are also examined by polyacrylamide disc electrophoresis. The range of usefulness of muscle myogens in species identification, and equally significantly, their value in establishing phylogenetic relationships of closely related groups, as the genusOncorhynchus, are discussed. The myogen patterns ofO.ketaandO.gorbuschafrom the Asiatic and North American coasts were found to be identical, further supporting the concept of absolute species specificity of these patterns.