ADH7 (alcohol dehydrogenase 7 (class IV), µ or ? polypeptide), is a 386 amino acid protein belonging to the zinc-containing alcohol dehydrogenase family and the class-IV subfamily. Seven different human ADH isozymes exist: three belong to class-I: ?, ? and ?; one to class-II: ?; one to class-III: ?; one to class-IV: ADH7; and one to class-V: ADH6. Encoded by a gene that maps to human chromosome 4q23, ADH7 localizes to the cytoplasm and is preferentially expressed in stomach, but, unlike other family members, is absent from liver. ADH7 is a homodimer that binds two zinc ions per subunit and contains nine exons. ADH7 participates in the synthesis of retinoic acid, a hormone important for cellular differentiation. Variations in ADH7 may be associated with alcohol dependence. ADH7 may also play a role in protection against aerodigestive tract cancer.