In mouse, the Sxr(b) deletion interval (delta Sxr(b)) maps to the small short arm of the Y chromosome and is known to contain gene(s) required for normal spermatogenesis; in particular, Spy, which is essential for the postnatal mitotic proliferation of spermatogonia. This deletion interval is approximately 1-2 Mb and contains eight known genes. In this paper we report the construction of YAC transgenic mice containing different regions of the delta Sxr(b) interval including Zfy1, Ube1y, Smcy, and Eif2s3. Two male and one female founder mice, transgenic for all four genes, were sterile. However, a fertile transgenic, carrying a full-length copy of the Smcy gene integrated into central Chr 12, was identified. Smcy is a highly conserved Y chromosome-located gene, encoding peptides corresponding to epitopes of the male-specific antigen, H-Y. The Smcy transgene was ubiquitously expressed in all organs and tissues tested in male and female carriers. Introduction of the transgene into an X Sxr(b)/O genetic background did not rescue the early arrest of spermatogenesis characteristic of these males. These data indicate that the presence of Smcy is not sufficient to restore spermatogenesis, making it a highly unlikely candidate for Spy.