Anti-Mullerian (AMH), a member of the transforming growth factor beta produced by immature Sertoli cells and, to a lesser degree, by granulosa cells from birth to the end of reproductive life, does not affect gonadal determination but has a negative effect upon gonadal development in both sexes. It blocks meiosis in fetal ovaries, leading to loss of germ cells and subsequent fibrous degeneration, and inhibits the transcription of aromatase and LH receptor. AMH also affects the development and function of the adult testis by blocking the differentiation of mesenchymal into Leydig cells and by independently decreasing the expression of steroidogenic enzymes. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.