OBJECTIVE: To evaluate the presence of circulating immunoglobulins that inhibit FSH binding to its receptor (Ig-FSHR) in patients with premature ovarian failure (POF). DESIGN: Non-randomized study. Blood sampling for determination of circulating immunoglobulins. patients Two hundred and forty-seven patients with POF and 60 normally menstruating women (controls). measurements Circulating immunoglobulins that inhibit FSH binding to its receptor were assessed by FSH-binding inhibition assay. RESULTS: Twenty-three out of 247 women with POF presented circulating immunoglobulins that inhibit FSH binding to its receptor. These patients had been previously diagnosed as ROS. Sixty control subjects proved negative. CONCLUSION: Determination of the presence of circulating immunoglobulins that inhibit FSH binding to its receptor could be instrumental in diagnosing the gonadotropin resistance ovary syndrome.