Gonadotrophin releasing hormone (GnRH) agonists have had a profound impact on infertility treatment by in vitro fertilization and related procreation techniques. Its combination with human menopausal gonadotrophin (HMG) for superovulation has increased the success rate in patients with premature luteinizing hormone (LH) surges, a poor response, endometriosis or polycystic ovarian disease. Although most in vitro fertilization (IVF) centres routinely use GnRH agonists for reasons of a better planning of activities, its superiority as a first-line treatment over the more conventional regimes of clomiphene citrate (CC)/HMG or HMG alone is still debated. An increase of the number and maturity of recovered oocytes was reported by most groups, but an inverse relationship between the number of oocytes and embryo quality and pregnancy rate after cryopreservation has been frequently mentioned. The possible complications of the combined use of a GnRH agonist with HMG include the formation of ovarian 'follicle' cysts and ovarian hyperstimulation syndrome; luteal phase defects are also common. Routine luteal phase support with progesterone and oestradiol valerate or human chorionic gonadotrophin (HCG) is required. GnRH agonists have proved to be safe drugs, side-effects are minor and sporadic and the congenital malformation rate in GnRHa/HMG treatment is comparable to the spontaneous rates reported in national IVF registers.