The role of CD80/CD86 and CTLA-4 in the pathogenesis of systemic lupus erythematosus and their clinical significance was investigated. By using RT-PCR technique, the expression of CD80/CD86 and CTLA-4 mRNA in peripheral blood mononuclear cells (PBMC) were semiquantitatively detected in 32 patients with active SLE. The results showed that the percentage of positive CD86 expression in active SLE was increased significantly as compared with normal controls (90.63% vs 60.00%, P<0.01). The mean level of CD86 mRNA expression in active SLE group was markedly higher than in the normal controls (0.6410+0.0174 vs 0.4510+0.0402, P<0.001). Compared with normal controls, the percentage of positive CTLA-4 expression and the mean level of CTLA-4 mRNA expression in active SLE group were both increased significantly (both P<0.01). There was no statistical differences in positive rate of CD80 and the average level of CD80 mRNA between the two groups (both P>0.05). It was concluded that the aberrant expression of CD86 and CTLA-4 might play an important role in the activity and development of SLE.