We studied the crosslinking of conventional nitrile rubber with metal peroxide at varying temperatures. Crosslink density, measured by swelling in the solvent until equilibrium, and the reaction rate increased with temperature, suggesting that crosslinking is a function of peroxide decomposition. At a specific reaction time, some peroxide remained in the unreacted form in the final product. This was not observed when the reaction temperature was sufficiently high to achieve total decomposition of the peroxide (190-200degreesC). When a carboxylated nitrile rubber was crosslinked, the same results were obtained. However, in this case, exclusively ionic or a combination of ionic and covalent crosslinks were generated, depending on the vulcanization temperature used.