Abstract: Two new heparin-binding proteins (HBP) in bovine seminal fluid are characterized. Both proteins are strongly correlated with enhanced fertility. The first protein exhibits a molecular mass of 31-kDa in SDS-PAGE electrophoresis, and has an N-terminal sequence, as well as internal sequences, closely correlated with deoxyribonuclease I-like protein. The second protein is identified as a tissue inhibitor of metalloproteinases, and has a 24-kDa molecular mass in SDS-PAGE electrophoresis under reducing conditions, and a 21.5 kDa under non-reducing conditions. N-terminal sequence information for both proteins is provided. Assays for these proteins may be employed to indicate bulls of higher fertility.