The mechanical behaviour and morphology of films prepared from poly(ethylene terephthalate), poly (butylene terephthalate) and polyamide-6 blends subjected to zone drawing and annealing with fixed ends are studied. It is established that as a result of simultaneous physical (crystallization, relaxation, partial melting) and chemical (solid state exchange reactions and condensation) processes substantial structural changes take place in the blends which affect their mechanical properties.