The aim of the present study was to evaluate the clinical efficacy of half-dose (50 mug) and further reduced dose (33 or 25 mug) gonadotropin-releasing hormone agonist (GnRH-a; triptorelin) long protocols for multifollicular ovarian stimulation (MFOS) for patients with high basal serum follicle-stimulating hormone (FSH) level undergoing in vitro fertilization and embryo transfer (IVF-ET). One hundred and two IVF-ET cycles performed in 84 infertile patients with high basal serum FSH (>10.0 mIU/ml) were included in this retrospective study. Study subjects were assigned to two groups: continuous half-dose GnRH-a long protocol (group A, n = 63) vs. further reduced dose GnRH-a long protocol (group B, n = 39) from half-dose at the start of GnRH-a to one-third or one-quarter dose after pituitary downregulation. Exogenous FSH or human menopausal gonadotropin was administered for MFOS in step-down mode, four or fewer embryos were transferred, and the outcomes of MFOS were compared between the two groups. Serum estradiol (E(2)) level on the day of human chorionic gonadotropin administration was significantly higher in group B (mean +/- standard deviation (SD): 1318.3 +/- 1120.4 vs. 2054.9 +/- 1773.5 pg/ml, p = 0.015). The number of transferable and good-quality embryos was also significantly higher in group B (mean +/- SD: 2.9 +/- 1.7 vs. 3.7 +/- 2.0, p = 0.027; 1.8 +/- 1.4 vs. 2.7 +/- 2.0, p = 0.020). No statistically significant difference in the outcomes was observed with respect to the dose of gonadotropins administered, the number of oocytes retrieved or the clinical pregnancy rate. In conclusion, GnRH-a long protocol with a reduced dose, tapered from the starting half-dose to a third or a quarter of the normal dose after pituitary suppression, may be beneficial for MFOS in IVF-ET patients with a high basal serum FSH level. A further prospective randomized controlled study on a larger scale is needed to confirm these findings.