The behavior of cinnamic acid in the presence of ion-pair reagents has been studied. Conditions have been chosen for the selective determination of cinnamic acid by capillary zone electrophoresis with normal and reversed polarity and spectrophotometric detection; the results have been applied for the analysis of drinks and milk hydrolysates. The influence of surfactants (sodium dodecyl sulfate, sodium octyl sulfonate) present in the buffer electrolyte on the efficiency of cinnamic acid determination is discussed.