Abstract A series of amino acid-derived sulfonate salts have been synthesized. They were found to inactivate efficiently and selectively human leukocyte elastase. The sulfonate salts of the methyl esters of L-norleucine, L-norvaline and L-valine were the most potent. The enzyme is inactivated irreversibly with concomitant release of bisulfite ion. The results demonstrate for the first time that ionic compounds can indeed function as novel inhibitors for the serine proteinases.