Coulometry and voltammetry at platinum and gold rotating disc electrodes (RDE) in aqueous media have been applied to N-substituted phenothiazines (chlorpromazine, fluphenazine, perphenazine, promazine, promethazine and trimeprazine). All display three anodic waves of one, one and two electrons, while piperazine derivatives consume a further two electrons in the side chain. All steps involve EC mechanisms, but all the primary products either disproportionate or react with the solvent and the sole and stable product is the sulphoxide, or the in-chain 1,4-dihydropyrazine for piperazine derivatives. Although any step may be used in voltammetric determinations, the first step gives the best results, as it also does for potentiostatic coulometry. Mechanisms have been elucidated, and the electrode kinetic parameters have been determined for the first two steps of each compound.