The aim of the present study was to delineate peptide sequences against which antisperm antibodies (ASA) are raised in immunoinfertile men. Using the phage display technology, seven unique and novel dodecamer amino acid sequences were identified that reacted with the sera of immunoinfertile men. The peptides were synthesized based upon these amino acid sequences and examined for their immunoreactivity with sera from ASA-positive immunofertile men (n=15) and ASA-negative fertile men (n=18) for IgM, IgG, and IgA class of antibody in the enzyme-linked immunosorbent assay (ELISA). All the seven synthetic peptides showed a significantly (P<0.001) higher mean absorbance values for IgG and/or IgA class of antibody with the immunoinfertile sera compared to fertile control sera. Three of the seven peptides demonstrated a stronger reaction (>2 SD units) with 27%–40% of immunoinfertile sera compared to fertile controls. These peptide sequences may find applications in the specific diagnosis and treatment of immunoinfertility and in contraceptive vaccine development. The phage display technique provides an exciting and novel technology to delineate sperm epitopes involved in immunoinfertility. Mol. Reprod. Dev. 72: 25–30, 2005. © 2005 Wiley-Liss, Inc.