Previous studies have shown that ovarian stimulation with clomiphene citrate (CC), human menopausal gonadotrophin (HMG), and multiple-dose gonadotrophin-releasing hormone (GnRH) antagonist is associated with a high rate of premature LH surge. This study assessed whether administration of the GnRH antagonist cetrorelix at an incremental dose or at a high dose (0.5mg) from the start could prevent premature LH surge. Couples with male factor or unexplained infertility who were going to undergo intrauterine insemination were randomized into two stimulation protocols. All women were stimulated with CC and HMG. In protocol A, cetrorelix was given at 0.25 mg per day when the leading follicles reached 14 mm, and increased to 0.5 mg when the leading follicles were 16 mm. With protocol B, cetrorelix was given at 0.5 mg per day when the leading follicles reached 14 mm. The primary outcome measure was the incidence of premature LH surge. Premature LH surge occurred in 21.6% of patients undergoing protocol A, and in 18.9% of patients undergoing protocol B. Cetrorelix at incremental dose or at 0.5 mg per day does not prevent premature LH surges associated with the CC/HMG/multiple-dose cetrorelix stimulation protocol.