A neutralizing epitope is identified within amino acids 40-64 of the mature form of human myostatin. Antibodies that bind this epitope with high affinity preferentially bind GDF-8 over GDF-11 and may he chimeric, humanized or fully human antibodies, immunoconjugates of the antibodies or antigen-binding fragments thereof. The antibodies of the invention are useful for increasing muscle mass, increasing hone density, or for the treatment of various disorders in mammalian and avian species.