In our study in hMG/hCG protocol, there is correlation between basal FSH level and number of oocyte retrieved (Rs = -0.4334, p = 0.039). FSH was not useful in predicting poor responders in an in vitro fertilization program where pituitary desensitization is routinely used. There is correlation between day 2, day 3 serum immunoactive inhibin level and number of follicle developed with hMG alone, or with hMG in conjunction with pituitary desensitization using a buserelin intranasal spray. The patients were divided by relationship between E2 peak and inhibin peak. The most of oocytes retrieved, oocytes fertilized and embryos cleaved were obtained when hCG was injected on the E2 peak day following the inhibin peak day. Inhibin concentration in aspirated follicular fluids was low and estradiol concentration was high in pregnant group. There is correlation between acceleration index of inhibin and number of oocyte retrieved in both protocols. Inhibin levels were significantly lower (P < 0.05) in women older than 36 years of age, although estradiol responses were not so influenced by age. These data suggest that: (1) In the early follicular phase, inhibin may be a valid index to predict ensuing follicular growth and follicular development. (2) The serum inhibin responses to maximal ovarian stimulation may be a sensitive and early index of declining ovarian function with advancing age. (3) Inhibin is an important factor for the diagnosis of pregnancy outcome.