MSVSP99 (mouse seminal vesicle secretory protein of 99 amino acids) is a member of the rat and mouse seminal vesicle secretory protein family. The gene encoding MSVSP99 is under androgenic control and we demonstrate here that this regulation involves a complex interplay of positive and negative regions. First, we show that the promoter region (-387/+16) sufficient to mediate a full androgen induction is a complex enhancer organized in two regulatory regions. These two regions are inactive individually and must act together to confer a 40-fold androgen induction to the MSVSP99 gene and androgen responsiveness is not only dependent on the presence of functional androgen response element (ARE) sequences but results from complex cooperations between ARE and non-ARE sequences forming an androgen response unit. Secondly, we characterized a new regulatory region (-824/-632) that decreases androgen-dependent transcriptional activity of the MSVSP99 promoter. This region, also able to repress the transcriptional activity of the heterologous thymidine kinase promoter, contains a functional promoter on the inverted strand (-826 to -387) and we identified a transcription initiation site located at position -639 with respect to the cap site of the MSVSP99 promoter. Sequence analysis of the flanking DNA also revealed that the MSVSP99 gene is surrounded by long interspersed repeated sequences called LINEs.