Erythropoiesis is the physiological process by which new red blood cells (erythrocytes) are produced in the bone marrow, a critical function for maintaining adequate oxygen transport in the bloodstream. This process is tightly regulated by the hormone erythropoietin (EPO), which is produced by the kidneys in response to low oxygen levels in the tissues. Testosterone has been shown to stimulate erythropoiesis, enhancing the production of red blood cells. This effect is mediated through the stimulation of erythropoietin secretion and a direct action on the bone marrow. Due to its ability to increase hemoglobin levels and red blood cell count, testosterone is sometimes used as a treatment for anemia, particularly in individuals with chronic diseases or in older adults with 'anemia of aging.' However, the use of testosterone for this purpose must be carefully monitored, as excessive erythropoiesis can lead to conditions such as polycythemia, characterized by an abnormally high concentration of red blood cells, which can increase the risk of thrombosis and cardiovascular events. The relationship between testosterone and erythropoiesis highlights the hormone's broader role in body physiology beyond its well-known effects on muscle mass and sexual function.