One-step extrusion proved to be an innovative technique for the production of poly(ethylene terephthalate)/bisphenol A polycarbonate (PET/PC) compatible blends and copolymers by transesterification in the presence of a small amount of catalyst which was mechanically dispersed on the polymers before their extrusion. This method provides possibilities for producing a variety of polymeric materials with different thermal and physico-chemical properties by varying the initial polymer compositions, concentrations and type of catalyst.