The study was undertaken to investigate the interaction between the release of endothelin-1 (ET-1) and prolactin (PRL) from human decidualized endometrial cells, and the effects of transforming growth factor (TGF)-b1 on the release of ET-1 and PRL from human decidual cells in the early stage of pregnancy. Stromal cells derived from human endometrial tissues were cultured on a type-1 collagen membrane in serum-free medium with or without 100 nmol/l oestradiol and 1 mmol/l medroxyprogesterone acetate (MPA) for 12 days. In addition, decidual cells of early pregnancy were cultured with or without TGF-b1 for 48 h. PRL and ET-1 levels in the media were measured by a specific enzyme immunoassay and RIA respectively.In decidualized endometrial cells induced by ovarian steroid hormones in vitro, PRL release increased and ET-1 release decreased in a time-dependent manner. Ovarian steroid hormones significantly attenuated ET-1 release. In the decidual cells of early pregnancy, TGF-b1 significantly attenuated the PRL release, whereas this growth factor dose-dependently increased ET-1 release. There was a significant negative correlation between the release of PRL and that of ET-1.These results demonstrate that the regulation of PRL release is quite different from that of ET-1 release in the human decidualized endometrial cells, and suggest that TGF-b1 has significant effects on PRL and ET-1 release in the human decidua of early pregnancy.