The Th2-type CC chemokine thymus and activation-regulated chemokine (TARC/CCL17) is one of the high affinity ligands for CCR4, a chemokine receptor predominantly expressed by Th2 cells. We examined serum and plasma concentrations of TARC/CCL17 in patients with systemic lupus erythematosus (SLE). Serum and plasma levels of TARC/CCL17 and plasma levels of monocyte chemoattractant protein-1 (MCP-1/CCL2) and macrophage-derived chemokine (MDC/CCL22) in patients with SLE were determined by ELISA. There were significant differences in the plasma concentrations of TARC/CCL17 between the patients with untreated SLE and treated SLE (p < 0.001), rheumatoid arthritis (RA) (p < 0.001), and healthy controls (p < 0.001). In addition, the plasma levels of TARC/CCL17 correlated with the class of lupus nephritis (higher in class I or II than in class III or IV). There was close correlation between plasma levels of MDC/CCL22 and TARC/CCL17. There was no correlation between plasma levels of MCP-1/CCL2 and TARC/CCL17. TARC/CCL17 may be a useful serological marker and may facilitate an assessment of the degree of disease activity in SLE. The development of SLE is closely related to the elevation of plasma TARC/CCL17 levels.