Firstly, there are molecules with very low variance between measured values, such as antipyrine or ketoprofen, within 0.5 log unit. Further molecules, such as carbazepine or theophylline, have reasonable variances within 1 log unit. The Table shows several molecules with variance within 2 log unitshence individual permeability measurements differ by more than 2 magnitudes. However, these large errors can be explained by the mixing of apparent and intrinsic permeability, that Fig. show to be several log units different for those molecules.