The effect of experimental inhibition of the erythropoiesis on ability of the erythroide "crown" cells of erythroblast islands of the bone marrow to respond to the erythropoietin by the increase of the proliferative activity was studied. It was discovered that this ability depended on the degree of the erythropoiesis inhibition and on the class of the erythroblast island maturity. In the culture of the erythroblast islands of the bone marrow on the second 24-hour period after transfusion polycytemia reproduction, the proliferative activity of the erythroid cells in response to brining of the erythropoietin to the culture increased more in the erythroblast islands of the first and second maturity classes than in the reconstructing the erythroblast islands. In the culture of the bone marrow erythroblast islands evolved on the fifth 24-hour period after the reproduction transfusion polycytemia, the erythroblast islands of the first and second maturity classes were absent, and the proliferative activity of the erythroid cells of the reconstructing erythroblast islands in response to brining the erythropoietin to the culture increased to a lesser degree than in reconstructing erythroblast islands of the bone marrow evolved on the second 24-hour period after the polycytemia transfusion reproduction.