Nickel strip 0.2–0.4 mm thick is a traditional magnetostrictive material due to its good adaptability to manufacture and corrosion resistance and an acceptable, though low, biased magnetostriction. However, some of the parameters of commercial nickel that are important for use in magnetostrictive acoustical-electrical transducers are inferior to magnetostrictive alloys designed specially for this purpose. Iron-cobalt-base (49–51% Co) Permendur (K49F) and iron-aluminum-base (12–14% Al) Alfer (Yu13) are the alloys most widely used in acoustic radiators. Alloys of the Ni −4% Co system have been developed and studied although they are not very popular yet. The present paper concerns ways of optimizing the composition of magnetostrictive alloys of the Ni −4% Co system.