Rheumatoid arthritis (RA) is a heterogeneous disorder with a spectrum of clinical severity ranging from mild arthritis to a crippling joint disease with involvement of internal organs. Carnitine is essential for muscle energy production and is required for the transport of long chain fatty acids and the acyl coenzyme A derivatives across the inner mitochondrial membrane. The levels of malondialdehyde (MDA), an index of lipid peroxidation, and the antioxidants copper-zinc superoxide dismutase (CuZnSOD), glutathione (GSH), ceruloplasmin (CP), catalase (CAT), and carnitine were assessed in 42 patients with RA and 24 control subjects. While plasma carnitine and erythrocyte CuZnSOD levels were significantly lower in the patients with RA compared with the control group (p<0.01 and p<0.001, respectively), the CAT level was not different from controls (p>0.05). Plasma MDA, CP, and erythrocyte GSH levels were significantly higher than in the control group (p<0.001, p<0.001 and p<0.01, respectively). MDA levels showed a positive correlation with CP and GSH levels (r=0.716, p<0.001 and r=0.492, p<0.01, respectively). However, MDA, GSH, and CP demonstrated a negative correlation with carnitine (r=-0.719, p<0.001; r=-0.559, p<0.01, and r=-0.635, p<0.001, respectively) in the patient group but not in controls. There was also a significant positive correlation between CP and GSH levels (r=0.561, p<0.01). However, neither CuZnSOD nor CAT levels demonstrated correlation withcarnitine, MDA, GSH, or CP levels. It was interesting that CAT activity was not altered and CuZnSOD activity decreased when compared with the control group. These results suggest that while CP, MDA and GSH levels increased, carnitine and CuZnSOD levels decreased, but CAT activity was unchanged.