An object of the present invention is to provide a medicament and method which is useful for prevention and/or therapy of arterial wall injury. According to the present invention, there is provided a method for prevention and/or therapy of arterial wall injury which comprises a step of administering the pyrazolone derivative represented by the following formula (I) or the physiologically acceptable salt thereof, or the hydrate or solvate thereof in a preventively or therapeutically effective amount to mammals including humans: ##STR00001## wherein R.sup.1 represents a hydrogen atom, an aryl group, an alkyl group, or an alkoxycarbonylalkyl group; R.sup.2 represents a hydrogen atom, an aryloxy group, an arylmercapto group, an alkyl group or a hydroxyalkyl group; or R.sup.1 and R.sup.2 are combined with each other to represent an alkylene group; and R.sup.3 represents a hydrogen atom, an alkyl group, a cycloalkyl group, a hydroxyalkyl group, a benzyl group, a naphthyl group, a phenyl group, or a phenyl group substituted with 1 to 3 substituents selected from the group consisting of an alkyl group, an alkoxy group, a hydroxyalkyl group, an alkoxycarbonyl group, an alkylmercapto group, an alkylamino group, a dialkylamino group, a halogen atom, a trifluoromethyl group, a carboxyl group, a cyano group, a hydroxyl group, a nitro group, an amino group and an acetamide group.