In this analysis of hematopoiesis, the regrowth of colony-forming cells in the bone marrow was examined in patients who had undergone medullary ablation and bone marrow transplant. The various stages of erythropoeisis and the factors that influence blood cell production are discussed: hematopoietic microenvironment, cytokines, tissue oxygen. Drawing on results from rodent and human studies, growth hormone factor (GH) function is explained, its interaction with insulin-like growth factors I and II (IGF I and II), and their effects on hematopoiesis. The aim of the study was to show the close link between GH, IGF I and II and erythropoiesis, because patients with GH deficit may present with partially impaired erythyroid proliferation that leads to the onset of anemia.