Serum inhibin A, inhibin B, pro-alphaC, and activin A levels in 30 women with idiopathic premature ovarian failure (POF), 30 postmenopausal women, and 30 age-matched fertile women were determined. Women with POF showed low levels of inhibin A and inhibin B, but not of activin A, whereas the levels of pro-alphaC were significantly higher than in postmenopausal women. Thus, the circulating level of pro-alphaC could be a marker for assessing residual ovarian function in women with POF.