PepT1, the product of the SLC15A1 gene, is expressed on the apical (luminal) surface of enterocytes, or intestinal epithelial cells, in the duodenum and jejunum. A member of the solute-linked carrier (SLC) family of transporters, it is an uptake transporter whose substrates include oligopeptides (di- and tri-peptides), pro-drugs (e.g., ACE inhibitors), antibiotics, and peptidomimetics (peptide-like molecules). Evaluation of interactions with PepT1 is recommended for these classes of drugs. A pH gradient (extracellular pH lower) drives proton-dependent uptake of compounds such as cephalexin and the pro-drug valacyclovir; inhibitors include the dipeptide glycylsarcosine (GlySar). Theoretically, drugs could be designed as substrates of PepT1, thereby enhancing their intestinal absorption.