39 patients which underwent an IVF-ET procedure at the INPer were divided in two groups. To one of them, progesterone was administered since the day of oocyte retrieval (group I), whereas the other group received progesterone 48 hours before hCG administration (group II). There were no statistical differences between the groups in the parameters analysed before the oocyte retrieval. There were statistical differences between the groups in progesterone levels in the day of oocyte retrieval in favour of group II, and in fertilization rate and transfer rate for group I. There were no valuable differences between the groups in pregnancy rate.