Capillary-zone electrophoresis (CZE) combined with an online concentration of the analytes by transient isotachophoresis was applied to the simultaneous determination of nitrite ion (NO₂^-) and nitrate ion (NO₃^-) in the cerebrospinal fluid (CSF) and serum of patients with various neurological disorders. Under the conditions employed, NO₂^- and NO₃^- in the examined CSF and serum were clearly detected as the corresponding peaks on the electropherograms. Nearly linear correlations were observed between the area and height of peaks and the concentrations of NO₂^- and NO₃^-, and their levels in the CSF and serum were calculated from standard curves obtained using authentic samples. These results showed that the NO₂^- and NO₃^- generated by the oxidation in vivo of nitric oxide (NO) significantly increase in the CSF of patients with some organic diseases in the central nervous system (CNS), thus suggesting that such diseases are widely accompanied by increases in the expression of NO synthase in the CNS.