We report the cloning and sequencing of a new cDNA sequence encoding a protein from the mouse seminal vesicle. An open reading frame of 297 nucleotides encoded a protein of 99 amino acids with a calculated molecular mass of 11.454 kDa. The first 21 amino acids constituted a signal peptide followed by 78 amino acids encoding the secreted protein. The cDNA sequence comprised a 3' untranslated region of 226 bp and the polyadenylation signal AATAAA, 19 bp upstream from the poly(A)+ tail. A high degree of homology was found between this protein and members of the family of seminal vesicle secretory (SVS) proteins, especially rat SVS VI. Northern blot analysis indicated the presence of a 0.7 kb mRNA species in the mRNAs of seminal vesicle tissue. Castration resulted in a marked decrease in the level of the 0.7 kb mRNA encoding the protein, whereas administration of testosterone to castrated males restored the 0.7 kb mRNA.