OBJECTIVE: To assess the pituitary responsiveness to GnRH stimulation of premenopausal women relative to age. DESIGN: Older and younger reproductive-age women underwent the GnRH stimulation test in the early follicular phase of the menstrual cycle. SETTING: Female subjects in an academic research environment. PATIENTS: Women aged 21 to 44 years consisting of normal volunteers and infertility patients. INTERVENTIONS: Gonadotropin-releasing hormone was administered intravenously between days 2 and 4 of the menstrual cycle. Blood samples were collected from -20 minutes before to 120 minutes after administration. MAIN OUTCOME MEASURE: Luteinizing hormone, FSH, inhibin, and E2 levels. RESULTS: No significant difference in baseline values existed between older and younger women with regard to LH, inhibin, and E2, but basal FSH levels were higher in older women. A significantly diminished percent of LH and percent FSH change above baseline occurred 30 minutes after GnRH administration in the older women compared with younger women. No change in inhibin or E2 levels could be detected during the sampling period. CONCLUSIONS: The present study demonstrates marked attenuation of the acute pituitary LH response (sensitivity) to GnRH stimulation in older women when compared with a younger cohort.