text: Since the first publication by Kansy and coworkers, several companies developed their own versions of the assay.  Early models incorporated iso-pH conditions in the compartments separated by a simple lipid membrane; subsequently, commercial products were introduced which incorporated more sophisticated lipid membranes.  The commercial products helped ensure that medicinal chemists across different corporate labs within a worldwide organization used the same standardized methodology, reagents and obtained equivalent system performance as demonstrated with a set of test compounds.  This has proved very useful as various operational activities have been outsourced to other countries.