An improved mathematical model to represent the desorption curve obtained in a ZLC (zero length column) experiment is derived and used to reinterpret previously published experimental data for benzene-hexane in NaX zeolite crystals. The resulting diffusivity data agree well with earlier liquid chromatographic data for the same experimental system (and also with vapour phase ZLC data measured at much lower concentrations). The parameters derived from the new model thus appear to be more reliable than those obtained from the original approximate analysis and the new model should therefore be adopted in future applications of the ZLC method to liquid systems.