The oxidation of a neuroleptic drug gabapentin (GP) by a new oxidant diperiodatocuprate(III) (DPC) has been studied in an aqueous alkaline medium. A minute amount (10(-7) mol dm(-3)) of ruthenium(III) is sufficient to catalyse the reaction. The reaction is first order in [DPC] in the presence of ruthenium(III). The order in [GP] is less than unity, whereas that in [Ru(III)] is unity. Increase in [OH-] accelerates the reaction rate. A plausible mechanism involving the active species of oxidant and catalyst is proposed. The reaction constants in the mechanism have been evaluated. (C) 2006 Elsevier B.V. All rights reserved.