The antinuclear factor (ANF) is present in most cases of systemic lupus erythematosus. We got 185 sera from the patients with erythematodes and other diseases, and normal control. They were each diluted from 20-fold to 1,280-fold. Mouse liver cell and human white blood cell were used as nuclear materials and indirect immunonuorescent technique was carried out. Circulating ANF was found in 37 sera from 40 patients with SLE, but in three sera from 38 DLE. Five sera from 117 other patients and normal control were ANF-positve. We also investigated the types of nuclear staining pattern, the staining titer, and antigen specificity on positive sera of SLE. The relation between ANF and clinical courses of SLE as following: in most cases, it showed high titer of antinuclear antibody and peripheral or shaggy pattern in active SLE, and low titer and speckled pattern in inactive SLE.