The effect of alpha- and beta-ecdysone was studied upon differentiation of eye and leg imaginal discs of Drosophila cultivated together with neural ganglia in the medium C-39. In the medium without hormone, eye and leg imaginal discs from larvae of the early 3rd instar are not capable of differentiation. In these conditions, eye imaginal discs from larvae of the late 3rd instar become pigmented in 5 weeks and leg imaginal discs form sometimes segmented limbs on the 4th week of cultivation. In the medium with alpha- and beta-ecdysone, eye and leg imaginal discs from larvae of the early 3rd instar reveal only initial stages of differentiation. The effect of beta-ecdysone concentration was studied upon differentiation of leg and eye imaginal discs from larvae of the late 3rd instar. On decrease of beta-ecdysone concentration from 0.05 down to 0.005 mug/ml, initial stages of differentiation of leg imaginal discs proceed at a slower rate but, then, more complete differentiation with the formation of chitin and neuromuscular tissue is observed. In eye imaginal discs alpha-ecdysone at a concentration of 0.5 mug/ml and beta-ecdysone at a concentration of 0.005-0.5 mug/ml induce the pigment accumulation already at the 1st week of cultivation and beta-ecdysone at a concentration of 5 mug/ml fully inhibits the formation and accumulation of pigment.