Erythropoietin (EPO) is a glycoprotein hormone produced by the interstitial fibroblasts in the kidney that signal for erythropoiesis in bone marrow. The increased activity of a hemocytoblast (RBC stem cell) allows the blood to have a greater carrying capacity for oxygen. EPO was first developed to counteract the effects of chemotherapy and radiation therapy for cancer patients. EPO also stimulates increased wound healing. Because of its physiological side effects, particularly increased hematocrit, EPO has become a drug with abuse potential by professional and amateur cyclists.