The kinetics of oxidation of L-histidine (His) by platinum(IV) in the absence and presence of copper(II) catalyst was studied using spectrophotometry in alkaline medium at a constant ionic strength of 0.1 mol dm-3 and at 25 C. In both cases, the reactions exhibit a 1:1 stoichiometry ([His]:[PtIV]). The rate of the uncatalyzed reaction is dependent on the first power of each of the concentrations of oxidant, substrate and alkali. The catalyzed path shows a first-order dependence on both [PtIV] and [CuII], but the order with respect to both [His] and [OH-] is less than unity. The rate constants increase with increasing ionic strength and dielectric constant of the medium. The catalyzed reaction has been shown to proceed via formation of a copper(II)_ histidine intermediate complex, which reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. Platinum(IV) is reduced to platinum(II) by the substrate in a one-step two-electron transfer process. This is followed by other fast steps, giving rise to the oxidation products which were identified as 2-imidazole acetaldehyde, ammonia and carbon dioxide. A tentative reaction mechanism is suggested, and the associated rate laws are deduced. The activation parameters with respect to the slow step of the mechanism are reported and discussed.