Women with PCOS (Rotterdam definition) whom anovulation is resistant to clomiphene citrate will receive recombinant FSH using the low-dose step-up protocol during only one cycle. Serum levels of estradiol, AMH, LH, FSH, inhibin B and ultrasound (U/S) parameters will be assessed twice a week until 3 days after appearance of > 1 dominant follicle(s).The starting dose of recFSH will be 50 IU/day. In the absence of criteria for dominance (see below) after 14 days at 50 IU/day, recFSH dose will be increased by 25 IU/day every 7 days until dominance is achieved. Dominance will be defined by the appearance of at least one follicle >10 mm growing at least 2 mm/day and serum E2> 100 pg/L. Ultrsound examination will performed with a 7-MHz transvaginal transducer (Sonoline Elegra, Siemens), in real time, according to a standardized protocol.Serum AMH levels will be assessed using the second-generation enzyme immunoassay AMH-EIA.