8-Azaguanine is a purine analog with the chemical formula C4H4N6O.

[5] It shows antineoplastic activity and has been used in the treatment of acute leukemia.

[2] The compound closely resembles guanine and appears to be competitive with it in the metabolism of living organisms.

[6] It has been shown to cause retardation of some malignant neoplasms when administered to tumors in animals.

[6] 8-Azaguanine was the first purine analogue discovered to inhibit experimental tumors in mice.