Abstract As has been shown, peptizing agents act in the mechanochemical and thermooxidative breakdown of elastomers as radical acceptors at low temperatures and as oxidation catalysts at high temperatures. Modern peptizing agents usually consist of thiophenols or aromatic disulfides combined with metal complexes (chelates) of Fe, Cu, and Co, as catalysts for the oxidative breakdown. The composition must be such as not to affect the mechanical properties, stability, and aging of compounds and vulcanizates. Peptizing agents have practically no influence on the vulcanizate properties. Mastication can be carried out as a separate step or as an integrated part of the mixing process. When mastication is integrated with the mixing process, vulcanizate properties like flex fatigue resistance are improved. The principles discussed enable the compounder to select the most favorable mastication and mixing procedure for any given situation.