Gonadotrophin-releasing hormone agonists (GnRHa) are used to prevent inadequate luteinizing hormone (LH) surges during ovarian stimulation in in-vitro fertilization (IVF). Dose studies for optimal dose assessment are lacking and unfavourable effects of the agonist on granulosa function and oocyte quality have been suggested. This double-blind randomized study was undertaken to assess the effect of four different doses to triptorelin on the degree of desensitization of the pituitary, and the recovery time of pituitary function after withdrawal of the agonist. Sixty-six regularly cycling women were allocated to a treatment group (n = 32) and a control group (n = 34). To assess the degree of pituitary desensitization and restoration in the treatment group, gonadotrophin releasing hormone (GnRH) challenges (100 microg, i.v.) were performed during treatment (day 17), and 2, 4 and 6 days after discontinuation of treatment. At the same time blood samples for oestradiol and triptorelin concentrations were drawn. In the control group a GnRH test was performed on day 2 of the menstrual cycle. Both pituitary desensitization during and pituitary recovery after agonist treatment, expressed as the LH response to exogenous GnRH, appeared to be dose dependent. As the use of reduced dosages still offers a considerable degree of pituitary suppression, studies on dose adjustments in the use of triptorelin, in ovarian stimulation in IVF are warranted.