It is found that in the process of cultivating the erythroblastic islets (EI) of rat bone marrow, the concentration of interleukin-6 (IL-6) increases in the culture medium. Stimulating erythropoiesis was observed on the 48th hour in cultures, the stimulation was characterized by the growth of endogenous erythropoietin and activation of formation of EI de novo and de repeto. The continuing increase in the concentration of IL-6 in the cultures at the 72nd hour of the experiment was accompanied by a decrease formation of islands de novo and a decrease in the absolute number of EI in culture.