With the use of the radioimmunoassay for growth hormone--releasing inhibiting factor (GIF), it was found that measurable amounts of GIF-like substance existed in the chorionic villi and decidua of pregnant women. The indirect immunofluorescent method revealed that the higher intensity of GIF-like immunofluorescence was presented in cytotrophoblasts rather than in syncytiotrophoblasts of the villi and in stromal cells of the decidua.