Hepatoblastoma differs from the adult type of hepatoma not only in pathology but also in clinical features. The ratio of fucosylation of serum alpha-fetoprotein (AFP), or the ratio of lentil agglutinin-binding fraction of serum AFP, was determined in eight patients with hepatoblastoma. The clinical data for the eight patients with hepatoblastoma were also reviewed. The ratio of fucosylation of AFP was significantly higher in all eight patients with hepatoblastoma, and it definitely decreased with the age at diagnosis. This finding suggested a correlation between fucosylation and a rapid rate of tumor growth, since there is a hypothesis that all hepatoblastomas originate early in fetal life.