Fetal testis--a very special endocrine organ.

The fetal testis is a special organ endocrinologically and not at all like a smaller version of the adult testis. Unlike the quiescent fetal ovary, its hormone production is very active. Besides testosterone it produces a special 'fetal gonadal hormone', the anti-Müllerian hormone. These two hormones together play a key role in the induction and regulation of male sexual differentiation. To meet these functional requirements the fetal testis has many unique features, especially as regards luteinizing hormone and follicle-stimulating hormone action, which discriminate it from the respective functions of the adult testis. In this article, some enigmatic features of fetal testicular endocrine function are concentrated on in an attempt to identify the most important questions for further research.