The decades long study of Mullerian Inhibiting Substance by numerous laboratories around the world has been driven, in large part, by pediatric surgeons and pediatric endocrinologists who have a keen interest in the molecular pathophysiology of genital tract defects that are visited upon their patients. A better understanding of the genes involved in the development of the normal reproductive tract in males and females should lead to a more rational analysis of the diseases caused by their abnormal function. Furthermore, a translation of this knowledge from the bench to the bedside may lead to clinically useful advances in the diagnosis and management of intersex patients. The molecular analyses of MIS and MIS receptor gene mutations and persistent Mullerian duct syndrome and the development of MIS ELISAs to evaluate testicular function as well as to follow the progress of gonadal tumors are several clear examples of successes over the years. It will be interesting to see what lies ahead.