Erythropoiesis is the fabrication process of erythrocytes and is located in bone marrow. After commitment, erythroid progenitors differentiate into erythroblasts and generate immature reticulocytes. Reticulocytes are then released in the blood circulation and mature into ertythrocytes. While absolute quantification of the proteome of erythroblasts, circulating reticulocytes and ertythrocytes have already been studied, a few is known about immature reticulocytes located in the bone marrow. Here, we mesured the absolute quantification of immature bone marrow reticulocytes and compare it to mature circulating reticulocytes and erythrocytes.