The electrochemical oxidation of theophylline (1,3-dimethylxanthine) at the pyrolytic graphite electrode has been investigated by voltammetry and controlled potential electrolysis and by isolation, identification and determination of the reaction products. The primary electron transfer process occurs by a 1-electron, 1-proton oxidation of the −N9=C8− double bond to give a free radical species which partially dimerizes to give a previously unreported compound, 1,3-(dimethylxanthyl-8)-1,3-dimethylxanthine. Part of the free radical is oxidized in a further 1-electron, 1-proton reaction to give 1,3-dimethyluric acid which is then immediately further oxidized in a 2e−/2H+ reaction at the −C4=C5− double bond to give 1,3-dimethylric acid-4,5-diol. This latter species is unstable and undergoes secondary electrochemical oxidation to parabanic acid and dimethylurea, and fragmentation to dimethylalloxan and urea and 6,8-dimethylallantoin and carbon dioxide.