Endometrial apoptosis increases from the proliferative phase through the secretory phase and peaks at menses. However, with the onset of pregnancy, the corpus luteum is rescued and stromal cells, instead of undergoing apoptosis, reorganize the cytoskeleton and then begin to differentiate. We hypothesized that in the presence of hormones (estradiol-17 and medroxyprogesterone acetate), chorionic gonadotrophin (hCG) as an early embryonic signal and induction of decidualization by dbcAMP, endometrial stromal cells are rescued by the regulation of proteins that inhibit apoptosis. The percentage of cells stained with annexin V, an early apoptotic marker, increased dramatically after cytoskeletal disruption with cytochalasin D compared with non cytochalasin D treated controls (P < 0.05). However, treatment of cells with hCG or dbcAMP in the presence of hormones significantly (P < 0.05) decreased the percentage of annexin V stained cells compared with cells treated with cytochalasin D alone. This inhibition was further confirmed by immunodetection of cleaved caspase-3 and TUNEL staining. The inhibition of apoptosis by hCG and dbcAMP was via the intrinsic pathway since the cytochalasin D treated cells stained intensely for Bax while the cells treated with hormones, hCG or dbcAMP stained predominantly for Bcl-2. Treatment of cytochalasin D treated cells with hormones and dbcAMP resulted in an increase in the secretion of IGFBP-1 and prolactin. Treatment of cytochalasin D treated cells with recombinant IGFBP-1 and prolactin also inhibited apoptosis. These data suggest that under in vitro conditions, both hCG and the induction of decidualization play a direct role in preventing uterine stromal cells from undergoing apoptosis. Furthermore, this inhibition of apoptosis may be mediated in part by IGFBP-1 and prolactin and the alteration in the expression of Bcl-2 and Bax.