The relationship of age to four aspects of ovarian function was investigated: daily progesterone levels, pulsatile progesterone secretion, follicular and luteal estradiol levels, and preovulatory estradiol levels. Daily progesterone levels decrease after age 40. Pulsatile progesterone secretion remains approximately stable with age, though older women have somewhat higher late luteal activity. Daily follicular and luteal estradiol levels decrease with advancing age, but preovulatory peak estradiol remains stable. Some of these changes undoubtedly have negative effects on fecundity, such as lower follicular estradiol and average progesterone, via effects on endometrial development and support. But other changes identified, such as stability of preovulatory estradiol levels and thereby presumptive capacity to stimulate a luteinizing hormone (LH) surge despite lower follicular and luteal levels, as well as increased pulsatile progesterone secretion around the time of implantation, appear designed to conserve and maintain function. Thus, ovarian endocrine function over the course of reproductive life represents a process of change, but not one of generalized functional decline. Rather, aging with respect to ovarian endocrine function may proceed on a track, or on multiple tracks, which are largely separable from the continual depletion of oocyte stores which occurs over the lifetime. ยฉ 1996 Wiley-Liss, Inc.