Abstract: The present invention relates to a novel assay or screen for identifying compounds with potential therapeutic value for the treatment of protein trafficking diseases such as Cystic Fibrosis (CF) and nephrogenic diabetes insipidus (NDI). The usual approach involves expressing the mutant form of the gene in cells and assaying function in a multiwell format when cells are exposed to libraries of compounds. Although such functional assays are useful, they do not directly test the ability of a compound to correct defective trafficking of the protein. To address this a novel corrector screening assay for CF has been developed in which the appearance of the mutant protein at the cell surface is measured as the assay output. This assay was used to screen more than 3100 compounds. This novel screening approach to protein trafficking diseases is robust and general, and may enable the selection of molecules that can be translated rapidly to a clinical setting.