OBJECTIVE: To determine whether elevated soluble Fas/APO-1 (sFas/APO-1) levels are associated with either autoimmune disease or evidence of flares in autoimmune disease. METHODS: Thirty-seven serum samples were retrospectively obtained from normal controls and patients with laboratory evidence of autoimmune disease activity. These samples were assayed for sFas/APO-1 levels by an enzyme-linked immunosorbent assay, and hospital medical records were retrospectively reviewed for clinical and laboratory characteristics of the patients. RESULTS: Soluble Fas/APO-1 levels did not correlate with clinical diagnoses or laboratory abnormalities. The mean and range of sFas/APO-1 levels were similar in systemic lupus erythematosus patients (including those with active disease), patients with other autoimmune diseases, and normal controls. CONCLUSION: These data strongly suggest that measurement of sFas/APO-1 levels is unlikely to hold clinical value or play a role in the pathogenesis of autoimmune disease.