Surface functionalization of polyethylene terephthalate film and track-etched microporous membranes was performed using organic synthesis at the solid-liquid interface. The hydroxyl chain ends, naturally occurring in the membranes or created by basic hydrolysis in the film, were activated by reaction with p-toluenesulfonyl chloride and then coupled to [4,5-(3)H]lysine used as a model of water-soluble bioactive molecules. The ratios of derivatization were determined by liquid scintillation counting of the radioactivity associated with the samples. The hydroxyl chain ends were further reacted with 4,4'-methylene di(phenyl isocyanate); the resulting surfaces equipped with sensitive isocyanate spacers were assayed as before using [4,5-(3)H]lysine. The ranges of derivatization were from 5 to 60 pmol of fixed amino acid per open surface unit (cm(2)). Some samples were also analyzed by X-ray photoelectron spectroscopy.