The hypothalamic neuropeptide, corticotrophin-releasing hormone (CRH), which is also produced by human endometrium, has been shown to induce its decidualization in vitro. This process, induced mainly by progesterone, has characteristics of an aseptic inflammatory reaction, and is modulated by locally produced pro-inflammatory factors. In humans, prostaglandin E(2) (PGE(2)) enhances while interleukin (IL)-1 inhibits the decidualizing effect of progesterone. The aim of the present work was to test the hypothesis that CRH might affect the decidualization of human endometrium interacting with these factors. Therefore, we studied its effects on the production of pro-inflammatory interleukins IL-1, IL-6 and of PGE(2) from human endometrial stromal cells in primary culture. The results strongly suggest that CRH decidualizes stromal cells, as judged by the appearance of cytokeratins and the production of prolactin, two established markers of decidualization. In parallel to its effect on decidualization, CRH also decreased the production of PGE(2), while it increased the production of IL-1 and IL-6. Exposure of endometrial stromal cells to IL-6 also caused decidualization. The data presented here suggest that endometrial CRH regulates the production of local modulators of decidualization, i.e. PGE(2), IL-1 and IL-6. We postulate that, through the regulation of these factors, CRH acts as a local fine-tuner of decidualization initiated by progesterone.