Oligosaccharide structures are attached to nearly all membrane and serum proteins, and their composition changes significantly in many diseases. We have analysed glycosylation of IgG heavy chains in 34 patients with juvenile chronic arthritis and 13 control individuals. IgG was purified from 0.7 ml of serum, separated by electrophoresis and transferred on to polyvinylidene difluoride (PVDF) membrane. Ricinus communis agglutinin (RCA I) and Bandeirea simplicifolia (BSA II) and Ulex europaeus (UEA I) lectins were used to measure galactose, N-acetylglucosamine and fucose, respectively. While there was no significant difference in average levels of galactose and N-acetylglucosamine, patients with juvenile chronic arthritis had 2.4 times more fucose attached to IgG heavy chains than control individuals. A different picture emerged when patients were divided into those with acute disease and those in remission. Patients in whom juvenile chronic arthritis was currently active had significantly lower levels of galactose than those in remission, in whom galactose levels were comparable to the control group. Fucose levels in both groups of patients were significantly higher than in the control group. These results show that whereas de-galactosylation is a good test to detect and measure the activity of juvenile chronic arthritis, increased fucosylation is a much more reliable measure for diagnosis of the disease itself.