We have previously cloned the human UDP-galactose ceramide galactosyltransferase (CGT, E.C. 2.4.1.45) cDNA. Its open reading frame encodes the key enzyme in the biosynthesis of the glycosphingolipids, cerebrosides and sulfatides, essential constituents of the myelin membrane of the central nervous system (CNS) and PNS. Expression of the CGT gene and of the myelin-specific proteins in the terminal differentiated oligodendrocyte of CNS and in Schwann cells of PNS is cell-specific and highly time-regulated. The CGT gene therefore is important in the differentiation program of the oligodendrocyte lineage. Here we report the structural organization and the chromosomal localization of the human CGT gene. The coding sequence is separated into five exons, which are distributed over >40 kb. The CGT locus was mapped to the distal region of human chromosome 4, band q26. The organization of the CGT gene and of the UGT (uridylglucuronosyltransferases) gene family suggests a correlation to functional domains of the encoded proteins.