We have cloned OCTN2, a new member of the organic cation transporter family, from a human placental trophoblast cell line. The hOCTN2 cDNA codes for a protein of 557 amino acids with twelve putative transmembrane domains. The octn2 gene, located on human chromosome 5q31, consists of ten exons. The OCTN2-specific transcript, 3.5 kb in size, is expressed widely in human tissues and in cell lines of human origin. At the level of amino acid sequence, OCTN2 is more closely related to OCTN1 than to OCT1, OCT2 and OCT3. When expressed heterologously in HeLa cells, OCTN2 mediates the transport of tetraethylammonium, a prototypical organic cation, in a pH-dependent manner. Several organic cations, including the neurotoxins 1-methyl-4-phenylpyridinium, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and methamphetamine, compete for the OCTN2-mediated transport process.