The inhibitor of apoptosis protein BIRC-5/survivin plays roles in both apoptosis and the regulation of chromosome-segregation/cytokinesis during mitosis. As the population dynamics of male germ cells are regulated by both proliferation (mitosis and meiosis) and apoptotic culling, we hypothesized that BIRC-5/survivin could be central to the regulation of spermatogenesis. We have analyzed BIRC-5/survivin expression throughout the seminiferous epithelial cycle of the rat. BIRC-5/survivin RNA and protein exhibit rhythms of expression throughout the seminiferous epithelial cycle. The highest levels of expression were found, by immunohistochemistry and in situ hybridization, to occur during the long first meiotic prophase of spermatocytes. Cytoplasmic abundance declined at metaphase and reappeared at anaphase. Some BIRC-5/survivin expression was also found to occur in interstitial Leydig cells. BIRC-5/survivin protein levels were up-regulated in vitro by the paracrine, Stem-Cell Factor, that is known to regulate both proliferation and apoptosis of germ cells and Leydig cells.