OBJECTIVE: To assess the ability of a GnRH antagonist (Cetrorelix, Asta Medica AG, Frankfurt, Germany) to prevent premature LH surges in an IVF-ET program using a simple protocol with one or two administrations. DESIGN: Controlled ovarian hyperstimulation was carried out in 17 women with three ampules a day of hMG, starting on day 2 of the menstrual cycle. A dose of 5 mg of Cetrorelix was administered when plasma E2 levels were between 150 and 200 pg/mL (conversion factor to Sl unit, 3.671) per follicle of > or = 14 mm. A second injection was performed 48 hours later if the triggering of ovulation was not decided in the meantime. RESULTS: Six patients received one injection and 11 patients received two administrations. Plasma LH levels showed a marked decrease and remained low after the administration of the GnRH antagonist. In six patients, the first administration of Cetrorelix was performed when a significant rise in LH plasma level was present. Even in these patients the GnRH antagonist was able to prevent an LH surge. The tolerance of the product was good. Six clinical pregnancies were obtained, of which four are ongoing (25% per ET). Two ongoing pregnancies were obtained after the transfer of a frozen-thawed embryo (35.3% per retrieval). CONCLUSIONS: The GnRH antagonist Cetrorelix in a simple, unique or dual administration, protocol was able to prevent premature LH surge in all of the 17 patients studied. If these results are confirmed by larger, randomized studies, the good tolerance and efficacy that we observed suggest a bright future for this product is assisted reproductive technologies.