The invention deals with a method for the assessment of the effect of excipients, pH and combinations thereof on the predicted absorption properties of low solubility compounds, comprising the step of assessing a change in a flux function for a combination of a low solubility compound and an excipient at at least one predefined pH value. The method allows a fast, accurate, and economic evaluation of an excipient being capable of optimizing the absorption of drug molecules, i.e. low solubility compounds. Furthermore, animal experiments can be excluded and use of compounds can be reduced in such evaluation. Thus, screening for future formulation efficacy (pH and excipient effects on solubility and permeability) of drug candidates can be justified, since the method is fast, compound-sparing, cost-effective, and reasonably accurate.