Objective: To evaluate the effect of low-dose GH-releasing factor (GRF) on folliculogenesis in regularly menstruating women. Design: Prospective clinical trial where individual patients served as their own control. Setting: Outpatient Reproductive Endocrine/Infertility Clinic of the Los Angeles County-University of Southern California Medical Center, Los Angeles, California. Patients: Seven regularly menstruating women. Intervention: During treatment cycles, subjects received 100 mu g SC GRF on cycle days 2 to 11 and were observed during a control cycle. Main Outcome Measures: Follicle number and diameter, as well as endometrial thickness were ll assessed by vaginal ultrasound and blood was obtained for serum FSH, LH, E(2), P, GH, insulinlike growth factor 1 (IGF-1), and insulin-like growth factor binding protein-3. Results: During cycles treated with GRF, GH, and IGF-1 levels were normal. However, follicular growth rates and E, to FSH ratios were significantly higher. The day of the peak E, to follicular diameter ratio after GRF was earlier than in control cycles. Endometrial growth rates were also greater with GRF. Conclusions: Our data, although preliminary, support the hypothesis that low doses of GRF may independently stimulate the ovary and enhance folliculogenesis.