In vitro fertilization treatment outcomes were compared prospectively in unselected patients with and without the addition of leuprolide acetate to gonadotropins for ovarian hyperstimulation. While the leuprolide patients required greater quantities of exogenous gonadotropins to achieve ovarian stimulation, significant improvements in the fertilization, implantation, and spontaneous abortion rates were observed compared with patients not receiving leuprolide. The ongoing pregnancy ("take home baby") rates per aspiration with and without leuprolide were 29% and 12%, respectively. Furthermore, the multiple pregnancy rate was markedly increased in the leuprolide group (44% versus 8%), suggesting that the improved pregnancy outcome with pituitary suppression was due primarily to higher oocyte and embryo quality.