Four separate ethylene-octene copolymers of differing molecular weight and co-monomer content have been moulded against polypropylene at various temperatures between 120 and 200 degreesC. The adhesion, measured by a 90 degrees peel test, varied with the particular copolymer, but for all of them it varied with moulding temperature, showing a maximum at about 160 degreesC. It is argued that the temperature variation depends on the extent to which interpenetration of chains occurs in the interfacial region. This, in turn, depends on the recrystallization temperature of the polypropylene. The relative magnitudes of peel energy for the different copolymers can be understood in terms of the extent of plastic yielding necessary in order to transmit a critical stress to the interfacial regions during peeling.