A simple, rapid capillary electrophoresis-laser-induced fluorescence (CE-LIF) method for the assay of recombinant human erythropoietin (rhEPO) was developed, with a limit of detection (LOD) of intact rhEPO at subnanomolar concentration (up to 10 ng/ml or 3×10-10 M), which was among the lowest ones reported.High sensitivity was accomplished by precolumn derivatization with the noncovalent dye NanoOrange.CE separation and reaction conditions were carefully manipulated for avoiding microheterogeneity of glycoforms and inhomogeneity of multiple labeling products.The fluorescence signal was linear over the range of 10 ng/ml-10 μg/ml, correspondingto the detection requirement of rhEPO in biofluids and pharmaceutical samples, as demonstrated by a real sample analysis.The same method was also applied to the quantitation of lysozyme, ranging from 300 to 1,000 ng/ml.Although the salt in reaction mixtures showed a detrimental effect on the fluorescence of the derivatives, this method could tolerate certain amount of salt, extending its application in biofluid analysis.In addition, zero order fluorescence emission kinetics was obtained, indicating that the rapid decay of rhEPO was derived from self-quenching effect.