OBJECTIVE: To determine whether levels of soluble Fas (sFas) are elevated in patients with systemic lupus erythematosus (SLE) and correlated with clinical disease activity. METHODS: Serum samples were obtained from 62 SLE patients and 39 normal controls. We measured sFas levels using an enzyme-linked immunosorbent assay. Disease activity variables including Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) were examined. RESULTS: The mean age of the patients was 32.1 years (range 13~60 years) and the mean disease duration was 3.0 years (range 0.2~10.0 years); 1 patient was male (1.6%). The median serum sFas concentration was 610.0 pg/ml for SLE patients and 292.9 pg/ml in controls. The serum sFas concentration was significantly higher in SLE patients than in controls (p<0.001). The Receiver Operating Characteristics (ROC) curve showed that the area under the curve for sFas was 0.911. Using the cut-off value of 370.5 pg/ml, the sensitivity was 0.871 and the specificity was 0.846. However, we could not find any correlation between sFas levels and disease activity variables such as SLEDAI, complement, and anti-dsDNA antibodies. There was no significant difference in sFas levels between active (SLEDAI > or =8) and inactive (SLEDAI <8) SLE patients. CONCLUSION: These results suggest that sFas levels are elevated in SLE patients, but sFas does not reflect disease activity.