One of the first studies denying the involvement of hyperprolactinaemia in endometriosis-related infertility reported no differences in the mean prolactin serum level between 43 infertile patients with endometriosis (372 mIU/L, range 187–752 mIU/L) and 36 infertile patients with normal pelvic findings (333 mIU/L, range 124–767 mIU/L), both being in the normal range for the population (less than 540 mIU/L). This evidence concerns the gene PRL and hyperprolactinemia.