Antinuclear antibody (ANA) titres, anti-native DNA levels, serum haemolytic complement (CH50), and complement components C3 and C4 were determined in 550 serum samples taken from patients with active (311 samples) or inactive (239) systemic lupus erythematosus (SLE). Increased anti-DNA levels were shown in 82% of the samples from patients with active and in 57.8% of those from inactive, disease. Decreased levels of CH50, and C3, C4 were found in 37, 50, and 80% of the samples taken from active and in 22, 29, and 67% of those from inactive, disease, respectively. Positive ANA test was found in 94.7% of the patients with active and 87.9% of those with inactive, disease. Significant differences were found between the two groups for all parameters. The correlations were close between the values of anti-DNA antibodies and CH50, as well as between the levels of CH50 and C3. Relationship between anti-DNA antibodies and C3 levels, as well as between CH50 and C4 levels was also demonstrated. Six subgroups for expressing the positivity of five parameters, 32 patterns of positive parameters were found and their possible application were suggested. In combining these parameters and using appropriate patterns, their determination may be helpful not only for the diagnosis but also for the assessment of disease activity.