Abstract: Virus free platelets in vitro of potato cv. Favoritawere used for the experiments. The changes of en dogenous phytohormones GA₃, IAA, KT, BAP, ABA during microtuber formation in vitro were invest igated. The
results showed that ( 1) overall, endohormone content in roots was higher than that in shoots during the period from platelets culture to microtuber formation; ( 2) Endohormone contents varied at all stages of microtuber format ion, GA₃, IAA, KT, BAP content in platelets and ABA content in the roots at initial stage of microtuber induction ( after transfering to inducation medium and under light conditions for 2 days) was higher than that at the stage of platelet culture. GA₃, IAA , KT, BAP content in the roots and IAA content in the shoots were reduced at the stage of stoloniferous shoots development ( 3 days under dark condit ions) but ABA content and IAA content in the root had no obvious changes. GA3, KT and BAP content in the shoots risen again and GA3 and BAP content in the root continuously reduced at the stage of microtuber formation ( 7 days under dark conditions) . IAA and BAP content increased gradually, BAP in the roots, KT in shoots reduced, KT in the roots and GA₃ in the shoots were stable at the stage of microtuber development ( 14 days under dark conditions) .

Key words: Potato (Solanum tuberosum), Microtuber, Endogenous phytohormones