Müllerian inhibiting substance (MIS), also known as anti-Müllerian hormone (AMH), is a protein hormone that plays a crucial role in male sexual differentiation by causing the regression of the Müllerian ducts, which would otherwise develop into female reproductive structures. Produced by the Sertoli cells of the testes during fetal development, MIS ensures the proper formation of male reproductive organs by inhibiting the development of female reproductive structures in males.