Vesicular electrokinetic chromatography was used to investigate solute partitioning from the aqueous phase into dihexadecyl hydrogen phosphate (DHP) vesicles. Retention factors of neutral solutes are related to their partition coefficients between the aqueous phase and vesicles (K-VW). The K-VW of the aromatic test solutes were readily obtained from the slopes of the linear relationships between retention factors versus DHP concentrations. The technique offers the advantages of speed, automation, and small sample size for determination of partition coefficients. The K-VW values of 43 uncharged solutes were measured at below as well as above the phase transition temperatures. The logarithms of partition coefficients (log K-VW) of solutes at 71 C (above T-c) were slightly higher than those at 36 C (below T-c). The solvation characteristics of DHP were also studied using linear solvation energy relationships at the two temperatures.