Objective. To assess nucleosome plasma levels in patients with systemic lupus erythematosus (SLE) and to study the correlations with serum antinucleosome, anti-double-stranded DNA (anti-dsDNA), and antihistone antibody activities, as well as with disease activity (by the SLE Disease Activity Index [SLEDAI]).Methods. In a cross-sectional study, we assessed 58 SLE patients for their plasma nucleosome levels. Plasma nucleosome levels as well as serum antinucleosome, anti-double-stranded DNA, and antihistone antibody activities were assessed by enzyme-linked immunosorbent assay. SLE activity was evaluated using the SLEDAI.Results. The mean (.t SD) plasma nucleosome concentration in SLE patients was 52 2 159 ng/ml (range 5-1,180), and was significantly higher than that of the controls (16 2 8.8 ng/ml, range 8-52; P = 0.03).