Survivin is a novel inhibitor of apoptosis. It has been reported that survivin is expressed during fetal development and in cancer tissues, but its expression has not been reported in adult tissues. We investigated the expression of survivin in the endometria of women with regular menstrual cycles using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry, and compared these findings with Bcl-2, an apoptosis inhibitor. Survivin mRNA was detected by RT-PCR in all samples (nine of nine) of endometrium during the secretory phase, but in only four out of seven samples from endometrium during the proliferative phase, and in none of the atrophic endometrium. Immunohistochemistry demonstrated a survivin protein expression that was strongest in the nuclei of glandular epithelial cells during the late secretory phase. In the proliferative phase, glandular epithelial cells were not stained for survivin. The cyclic changes of survivin and Bcl-2 showed an inverse relationship, with Bcl-2 expression being strongest in the proliferative phase and survivin expression being strongest in the secretory phase. The up-regulation of survivin expression may be due to the concurrent rise in progesterone concentrations during the normal menstrual cycle. Moreover, survivin could play an important role independent of Bcl-2 in physiological homeostasis in the normal endometrium.