[Show abstract][Hide abstract] ABSTRACT: To clarify the possible role of oxytocin (OT) on ovulation and conception compared to Human Chorionic Gonadotropin (HCG), a randomized controlled trial was carried out. One hundred clomiphene citrate-resistant anovulatory women, who were referred from April 2004 to September 2006, to the gynecologic clinics of teaching hospitals in Tabriz, Iran, were randomly allocated into 2 equal groups to take either Clomiphene Citrate (CC) plus OT (5 IU) or CC plus HCG (10, 000 IU). The size and the number of follicles by vaginal ultrasonography determined the administration of HCG or OT. The serum progesterone concentration was measured to prove the ovulation. The ovulation and the pregnancy rate of the two groups were compared. Sixty-seven women completed the study. There was no significant differences between the two groups in the rate of ovulation (92% vs. 84%, respectively, p>0.05). No significant differences were noticed between the two groups in the mean number of follicles at the first month (p = 0.63), but at the second month, the OT group had significantly more follicles (p = 0.024). The rate of pregnancy was similar (16.4 vs. 18.3 at two consecutive cycles). The OT group had more pain than the HCG group (p<0.0005) and the HCG group had more hyperstimulation rate than the OT group (p<0.05). The findings of this study provided essential insights to the physiological roles of OT in human follicular development and oocyte maturation. Oxytocin administration in CC-resistant patients gave a unique opportunity to use alternatives to stimulate oocyte maturation, in comparison with HCG and was associated with a fewer side effects.