Surface functionalization of poly(ethylene terephthalate) (PET) film or track-etched membrane was performed using the methods of organic synthesis conducted at the solid-liquid interface. Basic hydrolysis in aqueous acetonitrile followed by permanganate oxidation in diluted sulfuric acid created new carboxylic chain-ends. These reactive functions were assayed as follows : (i) activation with water soluble carbodiimide; (ii) coupling to H-3-labeled amino acids; and (iii) liquid scintillation counting of the sample-associated radioactivity. Some samples were also analyzed by X-ray photoelectron spectroscopy. Depending on the experimental conditions (temperature and duration of treatment), about 1-2% of the surface repeated units could be functionalized without deterioration of the polymer bulk. This study establishes the best conditions for the covalent anchorage of bioactive substances on the PET surface.