Received December 14, 1999
Accepted January 15, 2000

Oocyte donation (OD) is a well established method of assisted reproduction for women with irreversibly infertility and with previous implantation failures after IVF. Although the pregnancy rates are very high, sometimes implantation does not occur even after various attempts. We report the first two cases of transfer of zona free blastocysts in oocyte donation cycles that developed to normal pregnancies and births. The patients had undergone three previous standard oocyte donation cycles with failure of implantation. Endometrium preparation was performed after suppression of the pituitary function, with estradiol valerate and progesterone at the day of oocyte retrieval. Normally fertilized embryos were cultured in Earle's culture medium until day 3 and in S2 medium until day 5. For each patient, the zonae of two fully expanded blastocysts were enzymatically removed with 0.5% pronase. Zona free blastocysts were transferred for the patients 2 hours later. On day 12 after transfer, pregnancies were confirmed with elevated serum leveIs of B-hCG. A gestacional sac with a fetal heart beat was seen by ultrasound 15 days later, in each patient. Normal healthy babies were bom at 38 and 39 weeks of pregnancy, respectively. This is the first report of successful pregnancies and births after oocyte donation and transfer of zona free blastocysts in humano It shows not only the feasibility of the treatment but also, opens a new alternative for the patients with repetitive implantation failure after OD cycles.