Tissue-specific cAMP-dependent phosphoproteins (pp45, pp40, and pp20) were detected in accessory gland. In the present study, we characterized and purified pp45. The purification procedure consisted of 3 steps including heat treatment, DEAE cellulose column chromatography and high performance liquid chromatography (HPLC). The purified protein could be phosphorylated in vitro by the catalytic subunit of cAMP-dependent protein kinase and derived from the lumen of the accessory gland. The partial sequences of this protein were lso-Lys-Asn-Val-Ala-Lys-Ala-Glu-Arg-Asn-Met-His-Asn-Met-Leu-Arg and showed 6 amino acids sequence homology with Mst57Dc. Currently, we are performing cDNA library screening and making the antiserum of pp45.