The distribution pattern of sialylated glycoproteins in the hippocampal formation of 9-week-old and 29-month-old rats was examined using Maackia amurensis lectin, specific for Sia alpha2-3Gal, and Sambucus sieboldiana agglutinin specific for Sia alpha2-6Gal(GalNAc), and a monoclonal antibody for a linear homopolymer of alpha2-8-linked sialic acid. Each lectin and antibody showed different and characteristic staining patterns. On comparison of younger and older animals, different staining patterns were revealed. These results indicate that sialoglycoproteins with different sialyl linkages were expressed in distinct regions of the rat brain and their expression patterns changed with aging.