Humoral abnormalities are a significant feature of rheumatoid arthritis (RA) even if as seems likely, they do not represent primary phenomena. Thus, autoantibodies including rheumatoid factor, anti-perinuclear factor and anti-RA33 antibodies are important serological features of RA, although none are truly disease-specific. In addition, it has been shown that serum IgGs from RA patients with RA have an increased number of oligosaccharide structures attached to the Fc region whose outer 'arms' lack galactose [i. e. increased Gal (0)]. Measurement of Gal (0) has been shown to have clinical utility in the assessment and follow-up of patients with RA.