ChEBI: Homovanillic acid is a monocarboxylic acid that is the 3-O-methyl ether of (3,4-dihydroxyphenyl)acetic acid. It is a catecholamine metabolite. It has a role as a human metabolite and a mouse metabolite. It is a member of guaiacols and a monocarboxylic acid. It is functionally related to a (3,4-dihydroxyphenyl)acetic acid. It is a conjugate acid of a homovanillate.