Identification of the glycosyltransferase genes that are involved in the biosynthesis of glycoconjugates has opened up new avenues in glycobiology, the decoding of the function of sugar chains. Specific biosynthesis of branched N-glycan structures by glycosyltransferases functionally modifies target glycoproteins, as observed in the recognition of cancer cells. A mouse model with a specific defect in alpha1-6 fucosylation showed emphysema-like changes of the lung and severe degradation of lung alveoli that derived from the dysregulation of signaling through the transforming growth factor-beta receptor. Functional glycomics and the identification of target proteins will provide a new way to elucidate the nature of disease in the post-genomic era.