A new micro high-performance liquid chromatographic system has been developed, which determines catecholamines from directly injected human urine without any sample pretreatment. The system consists of a mixing junction for adjusting the sample to pH 8.5, a micro alumina precolumn for enriching catecholamines in the sample, and a dual electrochemical detector for selectively detecting catecholamines based on their electrochemical reversibility. The system is able to operate with directly injected body fluids and to determine simultaneously all of the four catecholamines with high precision.