The need for more innovative and readily orally bioavailable therapeutics that can be developed faster has driven the development of tools and strategies that will have a major impact on those needs. The application of the Caco-2 human epithelial cell line for use as a tissue culture model for permeability measurements that can be used to predict oral absorption effectively demonstrates this strategy. This article discusses some applications of the Caco-2 tissue culture model in pharmaceutical development. The development of an experimental program to characterize the endogenous gut peptide transport system is described, as well as its application to the understanding of the oral absorption of cephalosporin molecules. Other studies describe the use of permeability studies for a chemical series of drug candidates to predict their oral absorption in vivo. Finally, the application of the model to aid in the development of formulation strategies is discussed.