A dipeptide or tripeptide carrier system for active agent delivery to cells has an N-terminus natural amino acid and an active agent covalently bonded to a side chain of one of the remaining amino acid bases. The system is amenable to formulation as an oral administrant. The active agent being a therapeutic, a fluorescent dye, or contrast agent where the active agent has a molecular weight of less than 500 atomic mass units. An optional linker is provided intermediate between the active agent and the linking side chain.