Objective: To study whether minimal interference in the process of selection of the single dominant follicle may serve as the basis for a simplified ovarian stimulation regimen for IVF. Design: Single-center randomized pilot study. Setting: Tertiary referral fertility center. Patient(s): Fifteen normo-ovulatory patients with a regular indication for IVF. Intervention(s): Ovarian stimulation for IVF was begun with 100 or 150 IU/d recombinant FSH starting on cycle day 5. From cycle day 8 or later, cotreatment was begun with 0.25 mg/d GnRH antagonist. No luteal support was provided. Main Outcome Measure(s): Total number of dominant follicles and characteristics of the endocrine cycle. Result(s): Multiple follicle development occurred in five of eight patients in the 100-IU group and in all seven women in the 150-IU group. Follicular phase and luteal phase lengths were normal, but the endocrine profile was abnormal. Conclusion(s): A fixed daily dose of 150 IU recombinant FSH starting in the midfollicular phase resulted in ongoing growth of a restricted number of dominant follicles and sufficient oocytes retrieved to lead to ET. A marked reduction in the total amount of gonadotropins administered compared with standard treatment was achieved. Withholding luteal support did not exclude pregnancies. (C)2000 by American Society for Reproductive Medicine.