Erythropoietin (EPO) is a human protein hormone that is predominantly produced in kidneys. It plays a major role in the formation of red blood cells, a process known as erythropoiesis. EPO is commonly used to treat and prevent anaemia in nephrology and cancer patients. Today this pharmaceutical is produced as recombinant human EPO in animal cell cultures, especially in Chinese hamster ovary (CHO) cells. EPO is the leading biopharmaceutical with a world-wide market of about ten billion Euro per year. This hormone has a bad reputation in the public due to its abuse in unethical and illegal doping of athletes.