Abstract: The present invention discloses novel gonadal peptides with inhibin-like activity. The novel peptides include two gonadal peptides, one consisting of 52 amino acids, the other consisting of 92 amino acids. Both of these peptides were initially isolated from human seminal plasma. Both have now been chemically synthesized. The novel peptides are designated as alpha-inhibin-52 and alpha-inhibin-92. Sequence analyses show that the NH.sub.2 -terminal 31 amino acids of alpha-inhibin-52 are identical to the structure of the 31 amino acid inhibin-like peptide previously reported by Ramasharma, et al. (1984). Sequence analyses also show that the COOH-terminal 52 amino acids of alpha-inhibin-92 are identical to the structure of alpha-inhibin-52. The amino acid sequence of alpha-inhibin-92 is: ##STR1## .