Even though the existence of a transport process for intact peptides in the brush border membrane of intestinal and renal absorptive epithelial cells has been known for almost three decades, it is only recently that the molecular nature of the proteins responsible for the transport process has been elucidated. Two peptide transporters, PEPT 1 and PEPT 2, have been cloned. The cloned transporters catalyze active transport of intact di- and tripeptides and utilize a transmembrane electrochemical H+ gradient as the driving force. The characteristic of H+ coupling makes PEPT 1 and PEPT 2 unique among the transporters thus far identified in mammalian cells. In addition, the peptide transporters have immediate pharmacologic relevance because a number of peptide-like drugs are recognized as substrates by these transporters. Recently, cultured cell lines of intestinal and renal origin that express PEPT 1 and PEPT 2 have been identified. These cell lines are likely to facilitate studies on the regulatory aspects of the peptide transporters.