The effects of salmon gonadotrophin (GTH)on production of proges-terone, 17α-hydroxyprogesterone. 17α, 20β-dihydroxy-4-pregnen-3-one(17α 20βP),androstenedione, testostone and estradiol by vitel1ogenic ovarian follicles of Atlanticsalmon (Salmo salar)in vitro were examined. The breakdown of germinal vesicle ofoocyte did not occur in both incubations with 0.1 and lμg/ml GTH, only small a-mount of 17α20βP was produced by lμg/ml GTH incubation at the 10th day. The follic-les with 0. 1μg/ml GTH produced two-fold amount of oestradiol than that with 1μg/mlGTH incubation. Progesterone, 17α--hydroxyprogesterone, androstenedione and testo-sterone were produced by the stimulation of GTR in a dose-dependent manner. Theresults indicate that vitellognic follicles show differnt responss to low or high doseof GTH stimulation. Oesthradiol production is the major biosynthesis pathway of sex ster-oids by late vitellogenic follicles in Atlantic salmon and it is responsible for oocyte vi-tellogenesis. A low dose of GTH is more effective on stimulating oestradiol production.