We investigated a possible association between markers of immune activation and disease activity in 52 patients with systemic lupus erythematosus (SLE). Serum concentrations of neopterin, beta-2-microglobulin, 55 kD-type soluble tumor necrosis factor receptor, soluble interleukin-2 receptor and soluble CD8 were compared to the Index of European Consensus Lupus Activity Measurement (ECLAM). All markers of immune activation, except sCD8, significantly correlated with ECLAM. Stepwise multiple linear regression analysis revealed erythrocyte sedimentation rate and neopterin to correlate best with ECLAM (multiple correlation coefficient = 0.74, P < 0.001). The study shows that serum neopterin concentrations are a useful independent index for disease activity in SLE. The finding of enhanced concentrations of various parameters of immune activation in patients confirm a role of the T cell and macrophage activation in the pathogenesis of SLE.