The use of 2,2,2-trifluoroethanol-water mixtures for peptide separations by capillary zone electrophoresis (CZE) displays some advantages over aqueous solutions. First, the increase in viscosity reduces and stabilizes the running current and facilitates heat dispersion, with a consequent improvement in the number of theoretical plates. Second, the decrease in the dielectric constant leads to a modification of the dissociation constants of the ionizable groups. The consequence is a change in selectivity that, for several favourable peptide pairs, provides an increase in resolution. Third, the interaction of trifluoroethanol with the peptide modifies the Stokes radius in a manner strongly dependent on the peptide sequence. This can also be utilized for an increase in CZE performance. Fourth, the structural properties of 2,2,2-trifluoroethanol are particularly useful for an improvement in the separation of large apolar peptides. Finally, the use of trifluoroethanol strongly stabilizes the capillary coating.