The objective of the study was to investigate the role of endothelin-1 in the pathogenesis of scleroderma renal crisis in patients with systemic sclerosis. We used immunohistochemical analysis with anti-endothelin-1 and anti-von Willebrand factor antibodies in comparing kidney biopsies from patients with systemic sclerosis and scleroderma renal crisis (n = 14); from normal kidneys (n = 5); and from patients with typical hemolytic uremic syndrome and thrombotic microangiopathy (n = 5), antiphospholipid syndrome (n = 6), diabetic nephropathy (n = 5), minimal change disease with cyclosporine toxicity (n = 5), or nephroangiosclerosis (n = 5). Kidney biopsies from all systemic sclerosis patients presented specific lesions: glomerular lesions with thickened capillary walls (n = 6, 42.8%), mesangiolysis (n = 3, 21.4%), fibrin thrombi (n = 3, 21.4%), hypertrophy of juxtaglomerular apparatus (n = 5, 35.7%), arteriolar lesions showing mucinous intimal thickening and lumen mucoid occlusions (n = 13, 92.8%), proliferation of intimal cells (ie, "onion-skin" lesions; n = 13, 92.8%), fibrinoid necrosis (n = 3, 21.4%), and fibrin thrombosis (n = 4, 28.6%). Chronic lesions in large arteries showed modifications such as fibrous intimal thickening (n = 13, 92.8%). The pattern of endothelial staining for endothelin-1 in both glomeruli and arteriolar lesions appears to be specific for scleroderma renal crisis. Glomerular endothelin-1 staining without arteriolar staining was seen in hemolytic uremic syndrome; and isolated arteriolar staining (without glomerular staining) was seen in a number of conditions including antiphospholipid nephropathy, cyclosporine toxicity, and diabetic nephropathy. Endothelin-1 is overexpressed in glomeruli and arterioles of patients with scleroderma renal crisis, which suggests that endothelin-1 might be a therapeutic target in this condition.