The objective of this study was to explore the relationship between serum levels of ß2-microglobulin (ß2MG), which some studies suggest reflect disease activity in systemic lupus erythematosus (SLE), and various clinical and immunological markers of disease activity in SLE. Twenty-six SLE patients and 10 healthy controls were included. Disease activity was assessed by: SLEDAI, 24¿hr-proteinuria, circulating levels of complement C3, anti-double-stranded DNA (anti-dsDNA), ß2MG and various pro-inflammatory and anti-inflammatory cytokines (IL-6, IL-8, IL-10, IL-18) measured with a multiplex assay, IFN-a assessed with a reporter gene assay, and a combined expression score of 12 IFN-a inducible genes in peripheral blood mononuclear cells. Median serum levels of ß2MG were significantly higher in SLE patients vs controls (2.8¿mg/L, range: 1.1-21.6 and 1.2¿mg/L, range: 0.9-1.7, respectively, p¿