Erythropoietin (EPO) is one of the most successful biopharmaceuticals in history and is used for treating anemia of different origins.However,it became clear that EPO could also work in a neuroprotective,antiapoptotic,antioxidative,angiogenetic and neurotropic way.It causes stimulation of cells to delay cell apoptosis,especially in the central nervous system.In rodent models of focal cerebral ischemia,EPO showed an impressive reduction of infarct size by 30％ and improvement of neurobehavioral outcome by nearly 40％.A large animal model dealing with ischemia and reperfusion of the spinal cord showed that EPO could reduce the risk of spinal cord injury significantly.In addition,some clinical studies tested whether EPO works in real live clinical settings.One of the most promising studies showed the innocuous ness and improvements in follow-up,outcome scales and in infarct size,of EPO-use in humans suffering from ischemic stroke.Another study ended unfortunately in a negative outcome and an increased overall death rate in the EPO group.The most possible reason was the involvement of patients undergoing simultaneously systemic thrombolysis with recombinant tissue plasminogen activator.An experimental study on rats demonstrated that administration of EPO might exacerbate tissue plasminogen activator-induced brain hemorrhage without reducing the ischemic brain damage.This case shows clearly how useful animal models can be to check negative side effects of a treatment before going into clinical trials.Other groups looked in human trials at the effects of EPO on the outcome after ischemic stroke,relation to circulating endothelial progenitor cells,aneurysmal subarachnoid hemorrhage,traumatic brain injury,hemoglobin transfusion thresholds and elective first-time coronary artery bypass surgery.Most of the results were pos itive,but are based mostly on small group sizes.However,some of the most neglected facts when focusing on experimental setups of ischemia of the central nervous system are issues like age and comorbidities.It might be extremely worthy to consider these points for future projects,because EPO might influence all these factors.