Patients with polycystic ovary syndrome (PCOS) are highly sensitive to gonadotropins. In recent years a number of publications have shown that chronic low-dose protocols are effective in reducing complications, in particular ovarian hyperstimulation syndrome (OHSS), especially if recombinant human follicle stimulating hormone (rhFSH) is used. The aim of the present study was to compare the efficacy and safety of rhFSH (Gonal-F, Serono) versus urinary human FSH (uhFSH) (Metrodin, Serono) in a low-dose step-up protocol for ovulation induction in clomiphene-resistent infertile PCOS patients. Twenty PCOS patients were recruited in two centers for an open randomized comparative study. A starting dose of a 75-IU ampule of rhFSH or uhFSH was used for 14 days with an increment of 37.5 IU every 7 days. Human chorionic gonadotropin (hCG) (10,000 IU, Profasi, Serono) was administered if one to three follicles achieved a diameter of > or = 16 mm. Sonographic and hormonal (serum estradiol and progesterone) monitoring of the cycles was performed. All the six pregnancies induced were in the rhFSH group, but two of them ended with miscarriage. There were no differences between the two groups concerning the number of ampules used, the stimulation days, the estradiol levels on the day of hCG administration, and the progesterone levels 7 days after hCG administration. Three patients had grade II, and one patient grade III OHSS. In conclusion, our results support the literature data that rhFSH is superior to uhFSH regarding pregnancy rates, not only in in vitro fertilization cycles, but also with a low-dose protocol in patients with PCOS.