Immunoglobulin G-lacking galactose (Gal[0]) appears to be helpful in differential diagnosis of early synovitis, and correlates with disease activity in rheumatoid arthritis (RA). Its utility for RA monitoring and prognosis has been evaluated in the present study. Forty-eight patients with early RA were observed for 3 years. Hand radiographs were assessed according to Larsen and results were expressed as damage score (DS) and progression of damage score (PDS). Gal[0], DS, and PDS were evaluated at the onset of the study and after 1 and 3 years. The average values of Gal[0] in RA patients at the onset of the observation were significantly higher as compared to healthy controls (0.43 +/- 0.22 vs. -0.03 +/- 0.09, P < 0.05). The findings of Gal[0] after a 3-year follow-up were also higher as compared to healthy controls (0.37 +/- 0.21 vs. -0.03 +/- 0.09, P < 0.05). Radiological progression (PDS > 15) was observed in 16 patients. This group was characterized by a constantly high level of Gal[0]. The level of Gal[0] in patients without or with moderate radiological progression (PDS < 15) was significantly lower at the onset of the study and remained low during the observation. The relationship between Gal[0] and radiological progression was shown. The data thus far obtained suggest that Gal[0] may serve as an indicator for the disease course in patients with RA. Secondly, we cannot exclude the possibility that the constantly elevated level of Gal[0] causes erosions.