Luteal function, endometrial receptivity, endometrial prolactin and glycoprotein secretions, blastocyst-secreted immunomodulant factors and embryo quality are nowadays considered the main determinants involved in embryo implantation control. The endometrial factors are progesterone-dependent. Out of 128 cycles of ART (AIH-IU, GIFT, IVF-ET), performed in 67 women at the Dept. of Obstetrics and Gynaecology of Parma during the period 1986-1991, 31 conceptions were obtained (pregnancy rate: 24.21%), 7 of which miscarried (abortion rate: 22.58%). According to these data, ART high abortion rate is possibly connected with poor luteo-endometrial function and poor embryo quality. Controlled ovarian hyperstimulation is thought to inhibit embryo implantation after IVF-ET by decreasing endometrial receptivity. Such a situation can be treated either by exogenous progesterone administration or by tubal techniques (GIFT, TET) performed in non-tubal infertility. Both strategies showed to better endometrial receptivity. A delayed intrauterine embryo transfer at blastocyst stage, when cocultures allow to, is supposed to raise the implantation rate in tubal infertility by enhancing embryo selection and endometrial receptivity. This paper also reports preliminarily on the predictive value of beta-HGC and estradiol levels, as well as of endometrial thickness, on early pregnancy outcome.