The anti-implantation ac-tion of nylestriol in rabbit was studied.The changes of uterine cytosol estrogenand progesterone receptor (ER and PR)were analysed with the dextron-coatedcharcoal method. Plasm progesterone levelof early pregnant rabbits was measuredby radioimmunoassay. The results showed that oral nylestriol could obviously preventthe early pregnancy of rabbit by anti-implantation of blastocyst. The content ofER decreased in the nylestriol group (P<0.01). The content of PR in nylestriolgroup was lo...