The gene encoding MSVSP99 (mouse seminal vesicle secretory protein of 99 amino acids), an androgen-dependent protein specifically expressed in the mouse seminal vesicle, was isolated and sequenced. A mouse genomic library constructed in the λEMBL12 vector was screened using a full length cDNA probe. One genomic clone was selected, 7·4 kb of which were shown to contain the whole MSVSP99 gene. The complete sequence of the MSVSP99 gene (1·7 kb), plus 0·8 and 0·3 kb of the 5′ and 3′ flanking regions respectively, has been determined. The gene is composed of four exons interrupted by three introns. The size range for the four exons is 47–217 bp, while that of introns is 87–615 bp. The transcription start site was identified as an adenine residue located 21 nucleotides upstream from the ATG start codon. Putative TATA and CAAT boxes were identified, along with a number of regions that shared homologies with known regulatory sequences. These included androgen-responsive elements located in the promoter as well as in the gene sequence. Sequence comparisons with other androgen-responsive genes showed strong homologies between the MSVSP99 gene and the seminal vesicle secretory protein (SVS) family genes (rat SVS II, IV, V and VI). Moreover, some regions were found to be conserved between the MSVSP99 gene and the human semenogelin I and II genes.