The capillary zone electrophoresis of two common nucleosides, adenosine and inosine, was investigated. Both compounds were resolved in a 0.1 M sodium phosphate buffer, pH 7.5. Contrary to expectations, adenosine behaved at this pH - 5 pH units lower than the literature pK(a) - as a negative ion, migrating behind mesityloxide (neutral marker) when working in normal polarity mode. To confirm the migration order, peaks were identified from absorption maxima, by high-speed scanning detector. The change in electrophoretic mobility with pH was investigated for the nucleosides, and 10 other background electrolytes were tried to match the separation capabilities of the sodium phosphate buffer. Most inorganic buffers showed comparable separation, while organic, Good-type buffers lacked selectivity.