Galactose-deficient IgA1 (Gd-IgA1) attracts a lot of attentions as a critical effector molecule in the pathogenesis and progression of IgA nephropathy (IgAN) in recent studies. It has been suggested that several O-link glycans modified regions exist in the heavy chain hinge region of human IgA1 molecule andGd-IgA1 circulates in blood stream of the patients with the pathological condition of IgAN. The deposition of Gd-IgA1 in glomeruli is considered to be involved in IgAN (Multi-hit Hypothesis of Gd-IgA1). The measuring system using snail (Helix aspersa; HAA) lectin that is extracted from snail and Gd-IgA1 ELISA (Code: 27600 Gd-IgA1 (Galactose-deficient IgA1) Assay Kit using this antibody (KM55) have been used in numerous studies and it has been suggested that serum level of Gd-IgA1 in patients with IgAN is signicficantly elevated compare with the level of healthy subject or patients with renal disease other than IgAN in such studies. In addition, this antibody (KM55) can detect Gd-IgA1 in tissue by IHC technique differently from the feature of HAA lectin and it has been revealed that Gd-IgA1 specicillay exists in glomeruli of the patients of IgAN from the studies using this antibody. It has been expected that clinical significance of Gd-IgA1 wil be revealed by further studies using this antibody.