A series of 23 quinazolines and 5,6,7,8-tetrahydroquinazolines was evaluated for inhibition of bovine milk xanthine oxidase. The synthesis of four of these compounds has not been reported previously. Several 2-amino-4-hydroxyquinazolines, as well as 2-amino-4-mercaptoquinazoline, were effective inhibitors of this enzyme. 2-Amino-4-hydroxy-6-hydroxymethylquinazoline was a threefold better inhibitor than its pteridine counterpart, while 2-amino-4-hydroxyquinazoline-6-carboxaldehyde was the most potent compound studied.