In brief: Blood doping—the process of withdrawing an athlete's blood, holding it 9 to 12 weeks until hemoglobin levels return to normal, and reintroducing it into the body immediately before an important contest—is a controversial Procedure, and its ethicality and legality are debated throughout the sports world. This review of the literature concludes that although five early studies did not provide sufficient objective evidence to support its use, the majority of 13 new studies support the physiological rationale and efficacy of the use of blood doping to increase endurance capacity.