Endothelin-1 (ET-1), endothelin-2, and endothelin-3, a family of 21-aminoacid peptides, are potent, long-acting vasoconstrictors of mammalian blood vessels. Elevated levels of ET-1 have been found in the circulation of patients with various diseases, all of which have some degree of vascular involvement that is associated with endothelial cell activation. These diseases include systemic sclerosis, primary and secondary Raynaud's phenomenon, pulmonary hypertension, Buerger's disease, and Takayasu's arteritis. The role of circulating ET-1 in the pathogenesis of the vascular and fibrotic lesions in these conditions remains to be elucidated. This review focuses on the recent findings of the clinical significance and pathogenetic role of endothelin in collagen vascular diseases, especially in Raynaud's phenomenon and systemic sclerosis. Although the etiology of systemic sclerosis is unknown, a vascular pathogenesis is supported by a variety of clinical and laboratory observations. The fact that plasma levels of ET-1 are elevated in patients with systemic sclerosis and this elevation is more remarkable in patients with diffuse scleroderma compared with limited scleroderma patients might further support the vascular pathogenesis of systemic sclerosis.