A 19-year-old nulliparous hirsute woman was evaluated for the very high serum levels of testosterone (T) and estradiol (E2) measured in an outside laboratory. Menarche had occurred at 11 years and was followed by regular menses. We confirmed the high levels of T (9-16 ng/ml, nv 0.2-0.8) and E2 (>1,000 pg/ml, nv 30-120). LH and FSH were consistently high (73-118 mU/l and 18-29 mU/l, respectively; LH/FSH ratio=4.1-4.7) and responsive to iv GnRH (LH baseline=118 mU/I, 30 min=290; FSH baseline=25 mU/l, 30 min=46). The unstimulated values contrasted with those (LH=12, FSH=8 mU/I) measured in the outside laboratory, suggesting antigenically anomalous gonadotropins. 17-OH-progesterone was normal (0.5 ng/ml). After 1 mg dexamethasone, serum cortisol was normally suppressed (24-->0.4 microg/dl), T declined minimally (9-->8.6 ng/ml) and E2 remained high (>1,000 pg/ml). An exploratory laparotomy was performed, and two enlarged ovaries with multiple cysts as in a typical polycystic ovarian syndrome (PCOS) were seen. Before the wedge resection of the ovaries, hormones were assayed in the ovary veins (right ovary: T=30 ng/ml, Pg=17 ng/ml, E2=>5,000 pg/ml; left: T=14 ng/ml, Pg=14 ng/ml, E2=>5,000 pg/ml). Histologically, the follicle cysts showed luteinization of the theca interna; there was no evidence for ovary tumor in either ovary. After 21 days of 35 microg ethynyl-E2+2 mg cyproterone acetate (CA), E2=3,000 pg/ml, T=1.4 ng/ml, LH=10.5 mU/l and FSH=4.1 mU/I. After three cycles of the said therapy (but with 50 mg CA in the first 10 days of each cycle), E2 was 1,600 pg/ml, T 1.7 ng/ml, LH 7.1 and FSH 4.6 mU/I. Based on similarities with the phenotype of the alpha estrogen receptor knockout female mice (alphaERKO), one possible explanation for the puzzling clinical and biochemical picture of our patient is resistance of (alphaER to estrogens. This is the first case of PCOS with extremely high E2 and T. Thus, the differential diagnosis of high levels of E2 +/- T should include PCOS.