To enhance physical performance some athletes have used various methods to increase red cell mass. The methods include 1. blood doping or the transfusion of autologous or homologous blood or erythrocytes, 2. administration of EPO (erythropoietin) and 3. administration of synthetic oxygen carriers. These methods have been introduced in medical practice to improve physical function and quality of life in patients with low blood count from acute blood loss, cancer or renal disease. The methods, which lead to marked improved aerobic performance, are all prohibited under the World Anti-Doping Agency’s (WADA) List of Prohibited Substances and Methods. Blood doping has been in used over the last half-century but became less common when EPO was introduced in the 1980s. Since the introduction of tests for exogenous EPO it is likely that blood doping has become more common again. Blood doping and administration of EPO or synthetic oxygen carriers have severe potential side effects including hypertension, heart attack, stroke and embolism. Detection is possible for EPO and synthetic oxygen carriers. In 2004, a test was introduced for homologous blood transfusion. There is intense research ongoing to improve the specificity and sensitivity of the various detection methods. In many sports, individual haemoglobin levels are continuously monitored and maximal safety levels for competition have been introduced. With the advancement of gene therapy and gene transfer technologies it is likely that EPO gene doping will be used in the future. Detection research projects focus on identifying “finger-prints” that may differ from makers of endogenous EPO. The effects of EPO may be broader than erythropoiesis alone. E.g., EPO has been shown to influence angiogenesis which may improve local substrate delivery in heart and skeletal muscle.