Organic cation transporters function primarily in the elimination of cationic drugs in kidney, intestine, and liver [1-3]. The murine organic cation/carnitine (Octn) transporter family, Octn1, Octn2, and Octn3 is clustered on mouse chromosome I I (NCBI Accession No. NW_000039). The human OCTN1 and OCTN2 orthologs map to the syntenic IBD5 locus at 5q31 [1], which has been shown to confer susceptibility to Crohn's disease [4]. We show that the human OCTN3 protein, whose corresponding gene is not yet cloned or annotated in the human reference DNA sequence, does indeed exist and is uniquely involved in carnitine-dependent transport in peroxisomes. Its functional properties and inferred chromosomal location implicate it for involvement in Crohn's disease. (C) 2002 Elsevier Science (USA). All rights reserved.