Serum IgG and IgA are glycoprotein and significant glycoform abnormalities have been established in primary Sjögren's syndrome. The proportion of asialylated IgG is abnormally high in the patients, whereas IgA1 and IgA2 appear to be over-sialylated. This peculiarity might explain the defective binding of IgA to asialoglycoreceptors. Furthermore, the activity of alpha 2,6 sialyl transferase is higher in the IgA-producing B cells from the patients than in the controls, whereas the alpha 2,3 sialyl transferase operates in the former cells but not in the latter. The mechanism of this enzyme dysregulation warrants elucidation.