OBJECTIVE: To determine the correlation between total anti-oxidant capacity (TAOC)and lipid peroxidase (LPO)levels in serum and disease activity in systemic lupus erythematosus (SLE). METHODS: The study population consisted of 99 patients with SLE according to the 1982 revised ACR criteria and 83 healthy controls.The serum TAOC levels in 99 patients with SLE and 83 healthy controls by the ABTS(R) inhibition method (Randox Ltd,Antrim,UK)and serum malondialdehyde (MDA)levels in 37 out of 99 patients with SLE were measured.Anti-dsDNA antibody (anti-dsDNA),albumin,AST,ALT,cholesterol,uric acid and creatinine were mea-sured to determine the association with the serum TAOC levels.The correlation between the serum TAOC levels and nephritis in 27 cases with nephritis out of 99 SLE patients was also investigated.The SLE disease activity was determined by the SLE disease activity index (SLEDAI)at the time of sample collection. RESULTS: Compared to the controls (1.37 +/- 0.127mmol/L),serum TAOC levels were significantly decreased (1.29 +/- 0.124mmol/L)in SLE patients (p=0.001). And there was a negative correlation between serum TAOC levels and SLEDAI total scores in the SLE patients (r=-0.388,p=0.0001),but no significant correlation between TAOC levels and C3 and anti-dsDNA.Further,a significant difference (p<0.04)in TAOC levels was found in SLE patients with and without nephritis.In comparison with other parameters such as AST,ALT,and cholesterol which might change anti-oxidant level,there was no correlation between the serum TAOC levels and them,except for serum uric acid (r=0.387, p=0.0001),creatinine,and albumin (r=0.507,p=0.0001).Additionally,we couldn't find significant correlation between the serum TAOC levels and MDA. CONCLUSIONS: The serum TAOC levels correlate significantly with SLE disease activity and are associated with nephritis.Also,this study showed a significant correlation with serum albumin levels in these patients.Conclusively,the measurement of the serum TAOC levels in patients with SLE will provide useful information on SLE disease activity.