High performance liquid chromatography (HPLC) was applied to study the behavior of a series of 1-hydroxy-imidazole-3-N-oxides (HIO) in solution. Some thermodynamic parameters influencing solute retention were determined from the temperature dependence of the capacity factor (k). A linear relation was derived between k and molecular parameters considering intermolecular association, which was predicted and confirmed. ΔGadsvalues are also highly correlated with connectivity index, molar refractivity and Van der Waals volumes. Retention data for twenty closely related imidazoles were measured and analyzed in relation to hydrophilic parameters.