Gamete intra-Fallopian transfer (GIFT) was performed in 130 treatment cycles over a 17-month period. In 91% (118/130) of the cycles one or more oocytes were available for insemination in vitro and only GIFT cycles with supernumerary oocytes were included in the present study. Pituitary and ovarian suppression was achieved with buserelin followed by stimulation of multifollicular development by human menopausal gonadotrophin (HMG). Failure of supernumerary oocytes to fertilize was associated with a significantly reduced pregnancy rate (3/23; 13%) compared to cycles where fertilization occurred in vitro (35/95; 37%). These findings demonstrate that the outcome of IVF of supernumerary oocytes may be of particular diagnostic value in couples where the female partner has not conceived following treatment by GIFT after pituitary down-regulation with buserelin and ovarian stimulation with HMG.