Studies indicate that autoimmune phenomena might be caused by a failure to eliminate autoreactive lymphocytes. Therefore, we examined Fas antigen and bcl-2 expression and function in lymphocytes from human systemic lupus erythematosus (SLE) patients. Freshly isolated lymphocytes from patients with active SLE expressed more Fas antigen than did lymphocytes from patients with inactive SLE or from normal controls. They also showed characteristic DNA fragmentation after treatment with anti-Fas antibody. Expression of bcl-2 in T cells from active SLE patients was significantly higher than that in cells from inactive SLE patients and from normals. These data suggest that lymphocytes in patients with active SLE maintain an activated state in vivo. However, the role of Fas and bcl-2 expression in the regulation of lymphocyte survival in SLE is still unclear and further investigations concerning the role of these molecules in autoimmune phenomenon in SLE are needed.