Rheumatoid arthritis (RA) is a multisystem disorder in which immunological abnormalities result in symmetrical joint inflammation, articular erosion, and extra-articular involvement. The etiology of RA is still unknown, but a defect in the glycosylation of IgG may be involved in its immunopathogenesis. Several studies have shown a correlation between the amount of IgG lacking galactose and the activity of RA. IgG galactosylation has been shown to be a useful marker of early RA and an indicator of poor prognosis. Analysis of IgG galactosylation may offer an insight into disease pathogenesis and may also be useful in RA diagnosis.