Abstract: Adult human leydig cells to the number of 2×107 cultured in vitro were collected and injected into the musculi vastus medialis in patients with hypogonadism due tO various causes.No immunos、lppressive agent was used in all cases after transplantation.Results showed that all patients had a significantly increased level of serum testosterone and improved male sexual potency,and that 3 of them appeared to recover the secondary sexual characters.It is suggested that the transplantation of human leydig cells was a new,effective treatment for male hypogonadism.