The present invention provides a method for determining drug permeability, wherein the method comprises, for each reference drug of at least two reference drugs having (i) the same ionization state at a given pH and (ii) a known drug permeability determined by the same drug permeability testing technique, the calculation of a metric related to retention time of each reference compound eluted from a liquid chromatography column having an immobilized artificial membrane functional group. Then, based on each metric and each known drug permeability, drug permeability is expressed as a function of the metric. The method may further comprise the calculation of the metric related to retention time for a further drug eluted from the liquid chromatography column, the further drug having the same ionization state at the given pH and an unknown drug permeability, and an assessment of drug permeability for the further drug, based on the metric for the further drug and the function.