Infertile PCOS patients who ovulated under CC or metformin without pregnancy achievement will be enrolled and treated with three trials of COS plus IUI. All patients will be randomly allocated into two different groups (groups A and B). In group A, COS will be obtained using the same ovulatory agent (CC or metformin) employed in the previous ovulatory cycles, whereas in group B using gonadotropins in a low-dose step-up regimen.