Erythropoietin (EPO) promotes the production of red blood cells, the key factor in the regulation of the oxygen transport, and has been abused by athletes for performance enhancement in endurance sports. Current methods to detect EPO misuse are based on isoelectric focussing (IEF), double blotting, and chemiluminescence detection. A new approach utilizing SDS-PAGE mobilities of target analytes is presented. Employing two internal standards (novel erythropoiesis stimulating protein and recombinant rat EPO), the assay provides a tool which allows the calculation of relative mobility values for endogenous urinary EPO and recombinant epoetins (e.g., Dynepo) and, thus, the distinction of these analytes in doping control samples. A reference group of 53 healthy volunteers and samples originating from a Dynepo (epoetin delta) excretion study conducted with a single person were analyzed and led to a significant discrimination of endogenous urinary and recombinant EPO. A clear differentiation was accomplished over a period of four days post-administration of a single injection of 50 IU/kg body weight. Hence, the method may be useful as a screening procedure in doping control or as complementary confirmation tool to the established IEF assay.