The determination of biogenic monoamines by enzyme-catalyzed oxidation after electrophoretical separation on a microfluidic chip decreases their detection limits significantly. An amperometric system with a chemically amplified response for neurotransmitters and their metabolites is presented. The principle is the rapid cyclic oxidation of the analyte on the amperometric detector in the presence of the redoxactive enzyme glucose oxidase in the capillary electrophoresis buffer. With this approach, detection limits in the range of 10(-7)-10(-8) M could be reached. Because of the good linearity between the current response and the concentration of catecholamines and their metabolites at concentrations up to 300 muM, this method is attractive for the analytical detection at low concentration levels such as in biological fluids.