Dezaguanine is a broad spectrum guanine antimetabolite. This compound differs from guanine only in the substitution of a carbon for the 3-nitrogen of guanine. Dezaguanine must be converted to its nucleotides to be active. Dezaguanine nucleotides inhibit synthesis of guanine nucleotides, and can be incorporated into nucleic acids in place of guanine nucleotides; incorporation into DNA may be particularly important in the cytotoxicity of this compound. Addition of certain purines or purine nucleosides can prevent dezaguanine cytotoxicity in vitro. It has exhibited sufficient preclinical antitumor activity, particularly against rat and mouse mammary adenocarcinomas, slow and fast growing mammary tumors in mice and the human breast xenograft subrenal capsule implant system. It has completed one phase I trial.