“…Supporting the first hypothesis are the increased uterine RNA and general protein synthesis on Day 5 (Heald, 1976), the induction of implantation by uterine RNA extracts (Segal, Scher & Ko'ide, 1977 ; Lejeune, Puis¬ sant, Camus & Leroy, 1982b) and the secretion into the uterine lumen of specific proteins at Day 5 (Surani, 1977). On the other hand, stimulation of implantation by actinomycin D (Finn, 1974;Camus, Lejeune & Leroy, 1979) as well as the inhibitory influence on blastocysts of fluids from uteri of animals with delayed implantation (Psychoyos, 1973;Weitlauf, 1976Weitlauf, , 1978O'Neill & Quinn, 1981, 1983, stand in favour of a mechanism acting through release from inhibition. In rats and mice, implantation depends on a sequence of ovarian secretions (oestrogen, proges¬…”