Liposomes, which mimic biomembranes, were used as a pseudostationary phase in capillary zone electrophoresis. The decrease in the mobility of an analyte owing to the presence of liposomes reflected interaction between the analyte and the liposomes. Equations were derived to calculate the specific capacity factor K-s (the capacity factor, k' normalized to the liposome concentration 1 M) from the migration times and to estimate the difference in free energy, Delta(Delta G(0)), of the weak analyte/liposome interactions. The order of K-s values for the drugs tested was aspirin < salicylic acid < warfarin much less than sulfasalazine. The peptide TyrGlySerThrPro GlyCysCys interacted more strongly with the liposomes (K-s = 10.1 M(-1)) than did TyrGlySerThrProGlySerSer (K-s = 9.1 M(-1)) These results were similar to those obtained earlier by immobilized liposome chromatography.