Objective: The hemizona assay(HZA) is an established functional test that examines in vitro sperm-zona pellucida binding capacity with high predictive power for fertilization outcome in IVF. The objective of this study was to evaluate the value of the HZA as a predictor of pregnancy in patients undergoing controlled ovarian hyperstimulation(COH) and intrauterine insemination(IUI). Design: Prospective clinical study. Setting: Academic center. Patient(s): Eighty-two couples with unexplained or male factor infertility that underwent 313 IUI cycles. Intervention(s): Basic semen analysis and HZA were performed within three months of starting COH/IUI therapy. Main Outcome Measure(s): Hemizona index(HZI) and clinical pregnancy. Result(s): Overall, patients with an HZI of < 30 had a significantly lower pregnancy rate compared to patients with an HZI of ≥30(11.1%vs. 40.6%, respectively; P < .05; relative risk for failure to conceive: 1.5[confidence interval 1.2-1.9]). In all patients combined, and in the range of HZI 0-60, the duration of infertility(P=.000) and the HZI(P=.004) were significant determinants of conception(receiver operating characteristics(ROC) analysis). In couples with male infertility, the average path velocity and HZI were significant predictors of conception(P=.001 and P=.005, respectively, ROC analysis). The negative and positive predictive values of the HZA for pregnancy were 93%and 69%, respectively. Logistic regression analysis provided models of HZI(P=.021) and duration of infertility(P=.037) with highest predictability of conception in male factor and unexplained infertility groups, respectively. Conclusion(s): TheHZA predicted pregnancy in the IUI setting with high sensitivity and negative predictive value in couples withmale infertility. Results of this spermfunction test are useful in counseling couples before allocating them into COH/IUI therapy. Objective: The hemizona assay (HZA) is an established functional test that examines in vitro sperm-zona pellucida binding capacity with high predictive power for fertilization outcome in IVF. The objective of this study was to evaluate the value of the HZA as a predictor of Pregnancy in patients undergoing controlled ovarian hyperstimulation (COH) and intrauterine insemination (IUI). Design: Prospective clinical study. Setting: Academic center. Patient (s): Eighty-two couples with unexplained or male factor infertility that underwent 313 IUI cycles. Intervention (s): Basic semen analysis and HZA were performed within three months of starting COH / IUI therapy. Main Outcome Measure (s): Hemizona index (HZI) and clinical pregnancy. 30 had a significantly lower pregnancy rate compared to patients with an HZI of ≥30 (11.1% vs. 40.6%, respectively; P <.05; relative risk for failure to conceive: 1.5 [confidence interval 1.2-1.9]). In all patients combined , and in the range of HZI 0-60, the duration of infertility (P = .000) and the HZI (P = .004) were significant determinants of conception (receiver operating characteristics (ROC) analysis). In couples with male infertility , the average path velocity and HZI were significant predictors of conception (P = .001 and P = .005, respectively, ROC analysis). The negative and positive predictive values ​​of the HZA for pregnancy were 93% and 69% respectively. Logistic regression analysis provided models of HZI (P = .021) and duration of infertility (P = .037) with highest predictability of conception in male factor and unexplained infertility groups, respectively. Conclusion (s): The HZA predicted pregnancy in the IUI setting with high sensitivity and negative predictive value in couples withmale infertility. Results of this spermfunction test are useful in counseling couples before allocating them into COH / IUI therapy.