We have previously used a gene-transfer scheme to isolate a human genomic DNA fragment that determines expression of a GDP-L-fucose:beta-D-galactoside 2-alpha-L-fucosyltransferase [alpha(1,2)FT; EC 18.104.22.168]. Although this fragment determined expression of an alpha(1,2)FT whose kinetic properties mirror those of the human H blood group alpha(1,2)FT, their precise nature remained undefined. We describe here the molecular cloning, sequence, and expression of a human cDNA corresponding to these human genomic sequences. When expressed in COS-1 cells, this cDNA directs expression of cell surface H structures and a cognate alpha(1,2)FT activity with properties analogous to the human H blood group alpha(1,2)FT. The cDNA sequence predicts a 365-amino acid polypeptide characteristic of a type II transmembrane glycoprotein with a domain structure analogous to that of other glycosyltransferases but without significant primary sequence similarity to these or other known proteins. To directly demonstrate that the cDNA encodes an alpha(1,2)FT, the COOH-terminal domain predicted to be Golgi-resident was expressed in COS-1 cells as a catalytically active, secreted, and soluble protein A fusion peptide. Southern blot analysis showed that this cDNA identifies DNA sequences syntenic to the human H locus on chromosome 19. These results strongly suggest that this cloned alpha(1,2)FT cDNA represents the product of the human H blood group locus.