One week after ligating the vasa efferentes or the corpus epididymis in adult Wistar rats, we have studied the histological structure of the testes, measured their weights, as well as those of the seminal vesicles, and estimated F.S.H. and I.C.S.H. levels in the plasma through radioimmunoassay. Whereas ligating the corpus epididymis has not effect, ligating the efferent ducts damages the germinal line, without any damage on the Leydig cells; it also raises F.S.H. circulating level, if not I.C.S.H. level. We therefore confirm an inhibin production by seminiferous tubules, this hormone returning to the blood stream in the testis or rather in the head of epididymis as our research in progress suggests.