The amino-acid composition of actin, tropomyosin, myosin, L-meromyosin, and H-meromyosin has been determined by the Moore and Stein Chromatographic technique. The data obtained on the meromyosins when added up yield the amino acid composition of myosin. Tropomyosin and actin taken in equal proportion also approximate myosin, although the agreement with some of the amino acids is poor. Although not permitting the conclusion that myosin is a compound of actin and tropomyosin, the data strongly suggest a relationship, and do not rule out the possibility that actin and tropomyosin may be subunits in the myosin molecule.