Mca-(ala7,lys(dnp)9)-bradykinin is a sensitive fluorogenic substrate for ECE-1 (endothelin-converting enzyme-1). The incorporation of a (7-methoxycoumarin-4-yl)acetyl (Mca) fluorescent group and a 2,4-dinitrophenyl (Dnp) quenching group has resulted in a large fluorescence increase upon substrate cleavage.