Since 1997, alterations regarding the anti-doping rules of sport federations have led to the prohibition of new classes of substances such as plasma volume expanders, anti-estrogens, aromatase inhibitors and artificial oxygen carriers (. perfluorocarbons, cross-linked hemoglobins) besides the classical doping agents including stimulants, narcotics, anabolic agents, diuretics and peptide hormones. The determination of doping substances, which has been based mainly on GC-MS procedures, is more and more performed employing LC-MS and LC-MS/MS instruments. For instance, the classes of betablockers, diuretics, corticosteroids and newly proteins such as the cross-linked hemoglobin 'Hemopure' are effectively detected utilizing LC-MS(/MS) systems. The urinary identification of erythropoietin (EPO)-doping is accomplished by means of an assay composed by isoelectric focusing with subsequent visualisation of characteristic EPO bands with monoclonal EPO antibodies (double blotting).