The thermolysis of 60/40 mixtures of polyethylene (PE) and polystyrene (PS) was investigated at temperatures below 440 degrees C. Liquid yield from the mixture, 84.1%, was comparable to yields obtained with the individual polymers. The yields of styrene monomer, 57.1%, and alpha-olefins, 27.7%, increased over those obtained when the polymers were processed individually. A significant interaction was observed between the polymers in which the addition of PS enhanced the rate of thermolysis of PE. It is proposed that this enhancement was due to the abstraction of hydrogen from the PE fraction by polystyryl radicals. The result of this effect is to increase the rate of volatile production from the PE and increase the solubility of the residue in chloroform. The data also support a mechanism for dimer production other than the generally accepted 1,3 transfer.