Endothelin (ET) is a 21-residue potent vasoconstrictive peptide produced by vascular endothelial cells and formed from its precursor, big endothelin (big ET), by endothelin-converting enzyme (ECE). Here we report the cloning and functional expression of a complementary DNA encoding a rat ECE from endothelial cells. Rat ECE is a highly glycosylated protein consisting of 10 possible N-linked glycosylation sites, a zinc-binding domain, and a single membrane-spanning region. It has structural and sequence homology to neutral endopeptidase and Kell blood group protein, a putative neutral endopeptidase. Monoclonal antibody risen against purified rat lung ECE recognized broad glycosylated bands in membrane fractions prepared from both rat lung and COS cells transfected with a rat ECE expression vector. Expressed ECE was inhibited by phosphoramidon, but not by thiorphan. It also cleaved big ET-1 efficiently but not big ET-2 or big ET-3. Northern blot analysis revealed that ECE messenger RNA is widely expressed in many tissues.