Administration of gonadotrophin-releasing hormone (GnRHa) agonists, used in IVF short-term protocols to initiate follicular recruitment, may be restricted to the early follicular phase without any further risk of LH surge. However, consequences of an early discontinuation upon residual endogenous gonadotrophin secretion are still unknown. Here, the effects of early cessation of GnRH agonist upon gonadotrophin secretion and ovarian parameters of IVF cycles were investigated. A total of 230 normo-ovulatory women were prospectively allocated to one of the two regimens: decapeptyl-GnRH (100 microgram) was daily injected either from day 1 to the triggering of ovulation (group 1) or for the first 7 days (group 2). Exogenous gonadotrophins (150 IU) were administered on day 4 and 5 with a subsequent adjustment. Detections of free alpha subunit and dimeric LH were performed by highly specific 'two site' monoclonal immunoradiometric assays. The results show that early discontinuation of GnRH agonist administration was associated with a sharp decrease in both plasma free alpha subunit and dimeric LH concentrations while plasma oestradiol response to exogenous gonadotrophins was reduced. Other ovarian parameters and pregnancy rate were unchanged. These data indicate that endogenous LH secretion is maintained by a daily administration of GnRH agonist and may contribute to the final follicular maturation.