Objective: To study whether stem cell factor (SCF) and gonadotropin work synergisticly in superovulation stimulation of an in-vitro fertilization and embryo transfer (IVF-ET) program. Methods: Total cycles of 30 IVF-ET patients with regular menstrual period were studied. The same superovulation regimen was employed. Enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA) were used to determine the levels of SCF, follicular-stimulating hormone (FSH) and luteinizing hormone (LH) in follicular fluid (FF) during ooeyte pick-up (OPU) and in serum before and after superovulation. Results: FF-SCF of follicles with diameter over 20 mm were different in three groups [(2. 6±0. 4), (4. 7±0. 5), and (5.3±0. 9), respectively, P＜0. 01], whereas the total numbers of developing follicles (diametre≥5 mm) were similar. Conclusion: SCF and gonadotropin may have synergistic effects on the development of follicles during gonadotropin stimulation in IVF-ET program.