To assess the effects of disease activity of systemic lupus erythematosus (SLE) and high-dose corticosteroids on endothelial injuries, the significance of soluble endothelial cell protein C receptor (sEPCR) and soluble thrombomodulin (sTM) was analyzed. Serum levels of sEPCR and sTM were measured by enzyme-linked immunosorbent assay (ELISA) cross-sectionally in 97 SLE patients, 49 patients with other rheumatic diseases and 22 normal subjects. The changes in these levels upon corticosteroid treatment were also analyzed in 41 patients. The levels of sEPCR and sTM were both higher in SLE and other rheumatic disease patients than in normal subjects. When low-dose corticosteroids were used, both the level of sEPCR and the ratio of positive tests for sEPCR were significantly higher in active SLE patients than in inactive patients [median 2.30 ng/ml (range 0.00-147.10 ng/ml) vs 0.00 ng/ml (0.00-58.90 ng/ml) and 53.5 vs 13.0%, respectively] (P < 0.005). Moreover, the ratio of positive tests for sEPCR was higher after corticosteroid treatment in 9 of 19 (47.3%) SLE patients compared to other rheumatic diseases (3/22; 13.6%). Although the mean level of sTM was significantly higher in active SLE patients than in inactive patients, the ratio of positive tests for sTM was not affected by disease activity or corticosteroids. In conclusion, the positive test for sEPCR is a more sensitive biomarker than that for sTM in reflecting endothelial injuries caused by active disease and often by corticosteroids in SLE.