The effect of a diestrous GnRH treatment on fertility and prolificacy of embryo recipient hair ewes was studied using 10 Kathadin donors and 30 Black Belly recipients. All ewes were adult, dry and multiparous. Induction and synchronization of oestrus were carried out by FGA sponges during 14 days. Sponges were withdrawn at the same time in donor and recipient ewes. Superovulatory treatment was carried out with 20 mg of pFSH in decreasing doses (4, 4, 3, 3, 2, 2, 1 and 1 mg) at 12-h intervals, the sponge withdrawal coinciding with the 7th dose. In recipients, 200 IU of eCG were applied at sponge withdrawal. Donors received a 100 µg intramuscular dose of decapeptid GnRH 36 h after sponge withdrawal. Oestrus detection was realised by vasectomised rams from 20 h after sponge withdrawal, at intervals of 4 h. Donors were intrauterine inseminated with fresh semen 56 h after sponge withdrawal (100 x 106 spz/dose). Embryo recovery was realised 7 days after sponge removal. All embryos were morphologically evaluated and blastocysts were transferred in pairs to the uterine horn ipsilateral to an ovulated ovary by laparoscopy. At transfer, treatment group (n = 15), received 100 µg of decapeptid GnRH, whereas control group (n = 15) received a distilled water dose. The mean donors response was 11.4 corpora lutea (CL)/ewe, with a recovery rate of 85% and an embryo viability rate of 76%. The beginning of oestrous in donors, and in treated and control recipients were 25.6 ± 0.6, 25.8 ± 0.6 and 26.4 ± 0.6 h, respectively (mean ± SEM). Fertility was higher in GnRH-treated than in controls (80 vs. 46%; P < 0.05). Prolificacy was similar in both groups (165%). In conclusion, the application of GnRH in embryo recipient ewes at transfer increases fertility without affecting prolificacy.