The effect s of 4-androstene-3, 17-dine ( ADSD) and 17A-methy-l testosterone ( MT) via implantation on maturat ion of the female silver eel, Anguilla japonica and their kinetic effects on serum GtH levels, brain and pituitary GnRH levels were studied. Serum GtH levels increased during the period of 1- 5 days after implantation of ADSD, and the responses elevated w ith increasing times of implantation of ADSD. Implantation of MT, however, did not increase serum GtH levels significantly, except on the 15th day after 7 times of implantation. These results indicated that implantation of ADSD and MT stimulated the secretion of GtH, and there was a difference in effect between ADSD and MT. A single ADSD implantation significantly increased mGnRH contents in the brain and pituitary one day after treatment, but two days later, mGnRH contents in the brain and pituitary returned to the levels of the controls, indicating that implantation of ADSD stimulated the mGnRH synthesis and secretion. Thus, androgen have positive feedback ef fects at the brain and pituitary level to st imulate gonadal development in the female silver eel.