Early pregnancy factor, a glycoprotein, and platelet activating factor, a phospholipid, are early signals of pregnancy appearing during the preimplantation period. The aim of this study was to determine if the administration of platelet activating factor to rabbits would stimulate the production of early pregnancy factor and, if so, to ascertain the organs responsible. Early pregnancy factor was assayed after the administration of synthetic platelet activating factor to intact rabbits, rabbits that had undergone bilateral salpingo-oophorectomy, and isolated in vitro perfused rabbit ovary and/or oviduct. Although serum early pregnancy factor activity was detectable 30 minutes after platelet activating factor injection in intact rabbits, no activity was found in rabbits whose ovaries and oviducts had been removed. Perfusate early pregnancy factor activity was detectable only in the presence of both ovary and oviduct, and was first evident 120 minutes after platelet activating factor exposure. However, combined samples of perfusates from the ovary alone and oviduct alone expressed positive early pregnancy factor activity. Furthermore, the addition of platelet activating factor to either single or combined perfusates did not increase early pregnancy factor activity. Our data imply that platelet activating factor induces the production of ovary and oviduct early pregnancy factor components independently.