The immunosuppressive protein glycodelin A (formerly named PP14) is produced by human decidua and secreted in the maternal circulation. Glycodelin A concentrations in serum have been used as indicators of endometrial function. The purpose of this study was to investigate the effect of glycodelin A on human chorionic gonadotropin (hCG) and human placental lactogen (hPL) release by freshly isolated cytotrophoblasts (in vitro). Cytotrophoblasts have been prepared from human term placenta by the three-step trypsin-DNase dispersion method of villous tissue followed by a percoll gradient centrifugation step. When placed in culture, the isolated mononuclear trophoblasts differentiated into syncytial counterparts within 12-72 h after plating. Trophoblasts were incubated with varying concentrations (60-300 microg/ml) of glycodelin A. Glycodelin A was isolated and purified by chromatographic methods from amnion fluid. Supernatants of the trophoblast cell cultures were assayed for hCG and hPL by immunological methods. The release of hCG is increased in glycodelin A-treated trophoblast cell cultures compared to untreated trophoblast cells. Glycodelin A inhibits the production of hPL in vitro. Differences in Glycodelin A stimulated cells and untreated controls are statistical significant. hCG and hPL are markers for the differentiation process of trophoblast cells to syncytial trophoblasts. The results imply that glycodelin A secreted by decidualised endometrium modulates endocrine function, as well as the differentiation of trophoblasts in culture.