The 4(5)-aminosubstituted-5(4)-carboxyamido-1H-1,2,3-triazoles constitute a new class of monocyclic compounds as effective inhibitors of XO. In the past to these compounds the structure of 9-unsubstituted-8-azahypoxanthines was wrongly attributed. However some 8-azahypoxanthines obtained via a new annulation reaction have been described in this paper. The inhibitory activity of the title triazoles resulted greater than that shown by the corresponding 8-azahypoxanthines. The inhibitory competitive activity of 4(5)-n-pentyloxyoxalylamino-5(4)-carbamoyl-1H-1,2,3-triazole toward the oxidation of 8-n-pentylhypoxanthine disclosed that only one lipophilic pocket is present within the enzyme.