It is an object to provide a radical scavenger, an active oxygen-scavenging agent and the like, which are highly efficacious clinically and novel, and so as to attain the object, 3,4-dihydroxyphenylalanine derivatives such as N-β-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD) or pharmaceutically acceptable salts thereof are contained as an active ingredient.
