['To examine Mullerian Inhibiting Substance (MIS) as an emerging diagnostic marker of ovarian function.', 'Medline review of published studies pertaining to the role of MIS in assessing ovarian aging, predicting response to ovulation induction in preparation for in vitro fertilization, assessing risk of developing ovarian hyperstimulation (OHSS) before ovulation induction, and diagnosis of polycystic ovarian disease (PCOS).', 'The majority of published studies to date support a role for MIS as a marker of ovarian reserve. Specific cut-off values are dependent upon the particular assay used. Mullerian Inhibiting Substance may offer value in assessing risk of OHSS and diagnosis of PCOS.'] Is mullerian Inhibiting Substance an ovarian growth factor of emerging clinical significance?