Surges of luteinizing hormone (LH) that result in luteinization but occur prematurely with respect to the diameter of the leading follicle, prevent attempts to induce multiple follicular maturation for in-vitro fertilization (IVF) in a significant number of women. We examined the possibility of blocking premature LH surges by the administration of Cetrorelix, a potent antagonist of gonadotrophin-releasing hormone (GnRH), in a study including 20 patients, some of whom had previously shown premature LH surges. All patients were treated with human menopausal gonadotrophins (HMG) starting on day 2. From day 7 until the induction of ovulation by human chorionic gonadotrophin (HCG) the GnRH antagonist Cetrorelix was given daily. HCG was injected when the dominant follicle had reached a diameter of > or = 18 mm and oestradiol concentration was > 300 pg/ml for each follicle having a diameter of > 15 mm. Oocyte collection was performed 36 h later by transvaginal ultrasound puncture, followed by IVF and embryo transfer. The hormone profiles of these patients and the results of IVF and embryo transfer are comparable to those treated with GnRH agonists and HMG. However, less time and especially less HMG is needed in comparison to patients stimulated with a long agonist protocol. Hence, treatment with Cetrorelix proved to be much more comfortable for the patient. In this study we showed that combined treatment with gonadotrophins and the GnRH antagonist Cetrorelix is a promising method for ovarian stimulation in patients who frequently exhibit premature LH surges and therefore fail to complete treatment.