Of the analgesics examined, phenylbutazone and oxyphenylbutazone showed neither anodic nor cathodic activity, while codeine is oxidised by a single four-electron step and dihydrocodeine by a six-electron step to the same products. Electrode kinetic parameters have been evaluated, and the reaction mechanisms elucidated. Determination of codeine and dihydrocodeine by anodic voltammetry is simple and rapid, and gives relative standard deviations of 2â 3%, and is free from interference from adsorption on the electrodes in 0.1 mol l^{â 1} sulphuric acid. The influence of pH in the range 0â 11.5 has been examined.