Abstract
Prolactin-like immunoreactivity has been localized by an immunoenzymatic method in the decidual cells of the endometrium in cases of early (10 weeks) normal pregnancy, (12 weeks) molar pregnancy, (8--10 weeks) tubal pregnancy, and of a nonpregnant woman under progestogen (lynestrenol) treatment. A specific endocrine influence, predominantly progestogenic, rather than the implantation of trophoblastic tissue seems to be required for the appearance of prolactin-like immunoreactivity in the decidual cells of the endometrium.