The powder microelectrode technique is employed in the detection of ultra-low concentrations of dopamine (DA), which can be adsorbed and thus preconcentrated on the inner surface of a carbon black packed powder microelectrode. The apparent reversibility and kinetics of the oxidation of DA were found to improve significantly, and separation of the oxidation current peaks of DA and ascorbic acid (AA) reaches about 300 mV. In the presence of 0.6 mM AA in solution, the oxidation current peak due to 20 nmol of DA remains clearly evident. After correction of the background current of AA, the height of the oxidation current peak of DA oxidation is proportional to the concentration of DA in solution, and is not affected by the presence of large excess of AA. The low limit of DA detection is ca. 20 nM in acidic solution, and less than 1 mu M in neutral solution. Detection of DA in concentrations as low as 5 nM can be achieved after prolonged immersion of powder microelectrode in solution.