Abstract: The invention relates to N-aryl-azetidinones, their preparation process and their use as active serine elastase inhibitors.The N-aryl-azetidinones are in accordance with formula: ##STR1## in which R.sup.1 and R.sup.2 can be a halogen atom or an organic radical, R.sup.3 represents a halogen atom or another good starting group and R.sup.4 represents H or an organic radical.The compounds with R.sup.3 .dbd.Cl or OSO.sub.2 CH.sub.3, R.sup.4 .dbd.H and R.sup.1 .dbd.R.sup.2 .dbd.F or R.sup.1 .dbd.F and R.sup.2 .dbd.Br are irreversible and selective elastase inhibitors.