Trifluoromethylketone compounds of the formula: ##STR1## wherein R.sup.1 is C.sub.1-6 alkyl which has one or two substituents selected from carboxy, esterified carboxy and di-C.sub.1-6 alkylcarbamoyl; phenyl(C.sub.1-6)alkyl, the phenyl moiety of which may have halogen or nitro or amino substituents and the alkyl moiety of which may have carboxy or esterified carboxy substituents; halo-phenyl; morpholino; or morpholino(C.sub.1-6)alkyl, R.sup.2 and R.sup.3 are each C.sub.1-6 alkyl, X is --or --NH--, and ##STR2## and pharmaceutically acceptable salts thereof are useful for inhibiting human elastase.