Capillary zone electrophoresis (CE) under conditions of reversed polarity is used in conjunction with electrochemical detection (EC) at carbon fiber microcylinder electrodes for the selective and sensitive determination of uric acid in human blood serum. Comigration of anions with the electroosmotic flow is accomplished with reversed polarity and the buffer additive cetyltrimethylammonium bromide (CTAB) in a 2-(N-morpholino)ethanesulfonic acid (MES) buffer system, giving rise to rapid and sensitive analyses. Optimal buffer conditions (pH 7.0), detection potential (0.80 V vs. Ag/AgCl), and electrokinetic injection are employed to allow for maximal resolution and signal intensity. Amperometric end-column detection with a carbon fiber microcylinder electrode results in lower limits of detection for uric acid of about 25 nM (ca. 140 amol injected) without the need for decoupling. Linear calibration plots using uric acid standards in water and serum are obtained over a linear range from 5.00 x 10(-4) M to 2.50 x 10(-7) M. Uric acid concentrations obtained for human sera using the CE-EC approach described here are shown to compare favorably to the accepted laboratory values.