The use of hydrogen transfer agents and catalysts to improve the base-catalyzed decomposition of polychlorinated biphenyls (PCBs) was investigated. The reaction proceeded only in the presence of base, but the rate of PCB disappearance increased with increasing amount of hydrogen transfer agents and catalysts. Up to 99+% disappearance of 20 000 mg/kg Aroclor 1242 in paraffinic oil was achieved within 1-4 h at 340-350 degrees C. A three-step mechanism is proposed for the formation of biphenyl, the main product : (1) hydrogen species generated from the paraffin oil; (2) hydrogenation of aromatic catalysts (phenanthrene, anthracene, and alkyl naphthalenes) to form dihydroaromatics, or absorption of hydrogen by hexagonal forms of carbon (graphite or carbon black as present in scrap latex) or transition metals (zero-valent iron and stainless steel); (3) transfer of the hydrogen species to the activated PCBs. The product, biphenyl, may be degraded further or possibly form adducts or polymerize.