In this GastroPlus™ User Group webinar, we will discuss the validation of passive permeability estimates in MembranePlus based on molecular structure alone for a library of diverse compounds and describe the application of MembranePlus to fit intracellular efflux transporter affinity (Km) and GastroPlus™ PBPK models to provide a good estimate of the significance of efflux transporters on dose linearity of absorption, distribution, and excretion.