Ecdysterone, its 20-desoxy-derivative alpha-ecdysone, their 2-desoxy-derivatives ecdysterone 2, 3, 22-triacetate and preparation BTI-4 have been studied for their effect on [3H]-thymidine incorporation in different populations of animal and human lymphocytes. It is shown the ecdysteron and its analogs in concentrations of 10(-12)-10(-5) M take considerable stimulating effect on DNA biosynthesis in animal lymphocytes activated by polyclonal mitogens. The concentration of ecdysterone being increased to 10(-4) m one can observe complete inhibition of activating effect of polyclonal mitogens. Effect of the studied ecdysteroids did not considerably depend on their structure. In case of splenocytes the stimulating effect of ecdysterone on DNA biosynthesis is less expressed than in the case of activated thymocytes. Ecdysterone was established to have considerable inhibiting effect on DNA biosynthesis in the culture of activated Con A cells of lymphocytes in the peripheral blood of healthy donors.