Urea (8 M) treatment of salmon gonadotropin results in the dissociation of the hormone into two subunits. These subunits were separated using DEAE-cellulose chromatography and gel filtration on Ultrogel ACA 54, and studied for their molecular weights, electrophoretic, biological, and immunological properties. Molecular weights of the alpha and beta subunits were, respectively, 12,500 and 17,000 as determined by gel filtration and sodium dodecyl sulfate-gel electrophoresis. In anionic polyacrylamide gel electrophoresis, 7.5%, the alpha subunit, migrated more rapidly (Rf = 0.67) than the native hormone s-GtH (Rf = 0.38), and the beta subunit did not migrate. The biological activities of the alpha and beta subunits were less than 10% of the GtH. Reassociation allowed a 30% recovery of the initial biological activity. The immunological properties studied on two radioimmunological systems specifically directed against s- and cGtH, show that immunological determinants were connected with the beta subunit, which also possesses characteristics of zoological specificity.