GDP-L-Fuc:N-acetyl--D-glucosaminide ␣1-6 fucosyltransferase (␣1-6FucT) catalyzes the transfer of a fucosyl residue from GDP-fucose to the asparagine-linked GlcNAc residue of complex N-glycans via ␣1-6 linkage. These oligosaccharide structures are essential for the attachment of polysialic acid to the neural-cell-adhesion molecule, and its levels are useful for the differential diagnosis of hepatocellular carcinomas with respect to the microheterogeneity of ␣-fetoprotein. We have been successful in the purification and cDNA cloning of ␣1-6FucT from porcine brain and from a human gastriccancer cell line. In the present study, mRNA expression of ␣1-6FucT in various rat tissues and human cancer cell lines was examined, along with the expression of ␣1-6FucT mRNA and the induction by treatment with several cytokines. Northern-blot analysis indicated high expression levels of ␣1-6FucT in brain and gastrointestinal-tract tissues of normal rats, as well as for a number of lung-cancer, gastric-cancer and colon-cancer cell lines. Although various cytokines did not induce ␣1-6FucT mRNA, differentiation of a tumor cell enhanced the mRNA by 2-to 3-fold. These results may provide new insight into studies on ␣1-6FucT in terms of carcinogenesis or differentiation.