Desloratadine was determined in two dosage forms (tablets and syrup) with the use of the method of capillary isotachophoresis. Several electrolyte systems of varying composition and varying pH were tested. Two electrolyte systems were selected for the validation of the method and determination of desloratadine in real samples. In both electrolyte systems, the precision, correctness, linearity, robustness, and selectivity of the ITP method were evaluated. The pre-treatment of the sample prior to analysis consisted in dissolving and diluting the pertinent desloratadine-containing dosage form with demineralized water to the required concentration. This pre-treated sample was fed directly to the apparatus.