To test the hypothesis that the concentration of early follicular phase serum antim¨ullerianinullerian hormone (AMH) or m¨hibiting substance (MIS) is a useful marker of ovarian response and assisted reproductive technology (ART) outcome. Retrospective analysis of day 3 serum samples drawn before treatment. Private ART program. One hundred nine consecutive serum samples from women younger than 42 years of age who were undergoing ovulation induction for IVF. Follicular aspiration for IVF after ovarian stimulation with FSH in a downregulated cycle using GnRHa treatment. Correlations between day 3 serum AMH/MIS, E2, FSH, inhibin B levels, and IVF outcome (i.e., number of retrieved mature oocytes, number and quality of embryos obtained, ongoing clinical pregnancy rates). Multivariate regression analysis on categorical data was performed to describe a predictive model of clinical pregnancy outcome. Mean serum AMH/MIS value for clinical pregnancy (n = 38) was 2.4 ng/mL, in comparison to 1.1 ng/mL for those who did not become pregnant (n = 71). No differences were noted in mean values for day 3 FSH, inhibin B, or E2 between groups. Multivariate regression analysis demonstrated that day 3 serum AMH/MIS had the greatest independent contribution in predicting pregnancy outcomes. These data demonstrate a strong association between day 3 serum AMH/MIS level and IVF outcome in women younger than 42 years of age. Higher AMH/MIS concentrations are associated with a greater number of mature oocytes, a greater number of embryos, and ultimately a higher clinical pregnancy rate. Furthermore, AMH/MIS may offer greater prognostic value than other currently available serum markers of ART outcome. To test the hypothesis that the concentration of early follicular phase serum antim¨ullerian-in-ullerian hormone (AMH) or m¨hibiting substance (MIS) is a useful marker of ovarian response and assisted reproductive technology (ART) outcome. Retrospective analysis of day 3 serum samples drawn before treatment. One hundred nine consecutive serum samples from women younger than 42 years of age who were undergoing ovulation induction for IVF. Follicular aspiration for IVF after ovarian stimulation with FSH in a downregulated cycle using GnRH-a treatment. Correlations between day 3 serum AMH / MIS, E2, FSH, inhibin B levels, and IVF outcome (ie, number of retrieved mature oocytes, number and quality of embryos obtained, ongoing clinical pregnancy rates). Multivariate regression analysis on categorical data was performed to describe a predictive model of clinical pregnancy outcome. Mean serum AMH / MIS value for clinical pregnancy (n = 38) was 2.4 ng / mL, in compa risn to 1.1 ng / mL for those who did not become pregnant (n = 71). No differences were noted in mean values ​​for day 3 FSH, inhibin B, or E2 between groups. Multivariate regression analysis of that day 3 serum AMH / MIS had the greatest independent contribution in predicting pregnancy outcomes. These data demonstrate a strong association between day 3 serum AMH / MIS level and IVF outcome in women younger than 42 years of age. Higher AMH / MIS concentrations are associated with a greater number of mature oocytes , a greater number of embryos, and ultimately a higher clinical pregnancy rate. And, AMH / MIS may offer greater prognostic value than other currently available serum markers of ART outcome.