Since our previous study showed that the gene expression level of beta-1,4-galactosyltransferase (beta-1,4-GalT) V is only increased in mouse NIH3T3 transformant and that beta-1,4-GalT V preferentially galactosylates the GlcNAc beta 1 --> 6Man branch of oligosaccharides [Shirane ef al. (1999) Biochem. Biophys. Res. Commun. 265, 434-438], whether its gene expression is correlated with malignant transformation was investigated. Northern blot analysis of beta-1,4-GalTs I, II, III, TV, V, and VI and N-acetylglucosaminyltransferase (GlcNAcT)V in human cancer cell lines showed that the gene expression levels of beta-1,4-GaIT V but not other beta-1,4-GalTs are strongly correlated with those of GlcNAcT V whose activity was shown to increase by malignant transformation, These results indicate that beta-1,4-GalT V is involved in the galactosylation of highly branched oligosaccharides characteristic of malignantly transformed cells,