The etiology of the premature elevation of plasma progesterone (P4) on the day of hCG administration and the consequences on the outcome of IVF treatments remain controversial. Several evidences indicate that PL may affect IVF outcome by disturbing follicular environment, with adverse effects on oocyte maturation, fertilization or early embryo cleavage. Alternatively, PL can also adversely influence the endometrium, affecting implantation and development due to premature decidualization. Oocyte donation offers a powerful tool in the study of oocyte quality, since endometrial characteristics can be controlled and are comparable among the recipients. To gain knowledge about the effects of PL on oocyte quality, we analyzed the results of our oocyte donation program, in donors who repeated cycles presenting PL or not, serving as their own controls. Retrospective analysis. A total of 240 oocyte donation cycles performed in our centre between January 1st and December 31st 2003 where each women donated at least two times, with PL in one of the cycle and normal plasma P4 concentrations on the hCG day in the other, were analyzed. Stimulation protocols comprised luteal GnRH-agonist suppression followed by ovarian hyperstimulation with gonadotropins (large protocol). We considered PL those plasma P4 levels higher than 1.1 ng/ml the day of hCG administration. According to these categorization, the recipients (n= 289) were divided into two groups of patients that received oocytes from donors with: P4 < 1.1 ng/ ml (LP4 group n= 148)- and P4 ≥ 1.1 ng/ ml (HP4 group n= 141). The two groups were compared regarding donor cycle parameters (gonadotropin doses, stimulation length, serum E2 on the hCG day, total and mature oocytes retreived). Rates of fertilization, embryo cleavage and fragmentation, blastocyst development, implantation, number of embryos transferred and cryopreserved, as well as pregnancy and miscarriage rates were studied. Statistical analysis was performed by χ2- test and Student’s t-test for categorical comparisons. A p value < 0.05 was considered significant. Independently of the established groups, we evaluated the direct effect of P4 on all different variables by regression analysis. The recipient characteristics (age, waiting time until donation, endometrial thickness and male factor) did not differ significantly regardless the donor plasma P4 on the hCG day. We found statistical difference in the number of oocytes retrieved (18.2 ± 0.6 vs 20.8 ± 0.6; p= 0.003) and mature oocytes (16.9 ± 0.6 vs 19.4 ± 0.6; p= 0.005) between the groups. Results of the cycles are sumarized in the table. Tabled 1 Hereby we demonstrate that the premature elevation of the plasma P4 the day of the hCG administration during controlled ovarian hyperestimulation in our oocyte donation program has no negative impact on the oocyte and embryo quality parameters. If a deleterious effect of PL in the endometrium is induced, still needs to be demonstrated.