Sixteen normal pregnant woman at delivery were administered 10 mg of Metoclopramide (MCP) intravenously, and the Prolactin (PRL) levels in the maternal plasma and in the amniotic fluid were measured by RIA before and after the administration, and in the umbilical plasma after the administration. Eight other pregnant women at term were studied similarly without the administration of MCP and served as the control. In this experiment, there was a significant increase only in the maternal plasma PRL but not in the amniotic fluid PRL nor in the umbilical plasma PRL. Furthermore, by using an intrauterine pressure catheter and a maternal intravenous cannula we measured the amniotic fluid PRL and the maternal plasma PRL about every 20 minutes during 3 hours before and after the intravenous administration of MCP 10mg. The maternal plasma PRL increased promptly and remained high for 150 minutes, while there was no significant change in the amniotic fluid PRL. This obvious discrepancy supports the hypothesis that decidua is the source of amniotic fluid PRL and suggests an independent regulation of amniotic fluid PRL.