GnRH Associated Peptide (GAP) (25-53), human is the human gonadotropin-releasing hormone-associated peptide (GAP) 25-53 fragment (hGAP-25-53), can be used as immunogen to generate antiseras including MC-1, MC-2, and MC-3. GAP is joined to the luteinizing hormone-releasing hormone (LH-RH) sequence by a 3 amino acid processing site.