2-Mercaptoadenine 1-N-oxide was obtained from 4-aminoimidazole-5-carboxamidoxime and carbon disulfide. Methylation and oxidation afforded the 2-methylsulfinyladenine 1-N- oxide, which could be converted to the Bchloro-or the 2-hydroxyadenine N-oxides, none of which are available by direct oxidations. A comparison has been made of the reactivity of the 2-methylsulfinyl and 2-chloro groups in the N-oxides and in the corresponding free bases.