Results of carbohydrate analysis of serum IgG from patients with rheumatoid arthritis (RA) confirmed an earlier report that IgG from patients with RA is galactosylated to a lesser extent than IgG from healthy individuals. In contrast to the previous report, we found that the content of galactose in IgG from controls and RA patients was negatively correlated with age (P = 0.026 and P = 0.010, respectively). In RA patients, the IgG content of galactose was also negatively correlated with the pain index (P < 0.05) and was lower in the presence of rheumatoid factor (P < 0.05). No correlation was found between the galactose deficiency of IgG from RA patients and sex, race, duration of disease, packed red blood cell volume, radiographic grade, disability index, extraarticular manifestations, articular erosions, or treatment with steroids. Furthermore, no correlation was found between the galactose content of IgG and serum levels of IgM rheumatoid factor or the ability of IgG to bind IgM rheumatoid factor in vitro. Significant galactose deficiency was also detected in IgG from patients with systemic lupus erythematosus and Crohn's disease, which suggests that the defect in the galactosylation of IgG is a feature common to a variety of chronic inflammatory diseases. The biologic significance of this observation remains unclear.