Six women with unexplained longstanding infertility and regular menstrual cycles were studied. All had luteal structures identified at laparoscopy on normal appearing ovaries and normal plasma androgen levels. Daily or every other day determinations of FSH, LH, estradiol (E2), and progesterone (P) were performed in one cycle. The results were compared to similar data obtained in five apparently normal women. All six infertile women had normal patterns of E2 secretion, with a characteristic midcycle rise, followed by a normal sustained elevation of plasma P. Contrasting with the above were grossly abnormal secretory patterns of FSH and LH in five of six patients. Two types of alterations were observed. 1) Four women had plasma LH persistently higher than FSH, with absolute LH concentrations above control levels in three. Midcycle LH surges were identifiable in all four, while a FSH surge was present in only one. The LH to FSH ratio was consistently above 2. 2) One patient had plasma FSH and LH levels fluctuating between high normal and the menopausal range. At midcycle, there was a synchronized rise of both FSH and LH though not as high as on other occasions in the same cycle. This was preceded by an E2 rise and followed by P elevation. The latter type (no. 2) of endocrine changes have been previously observed in much older women, during menopausal transition. The study indicates that normal E2 and P secretion, suggestive of normal ovarian function, may occur in the absence of characteristic FSH and LH patterns. The abnormal gonadotropin patterns may well be causally related to the patient's infertility.