The hydroxyl chain ends (PET-OH) displayed on the surface of poly(ethylene terephthalate) film and track-etched membranes of two different porosities were assayed by derivatization with reagents containing H-3 and fluorine tags. After activation by tosylation, the resulting sulfonate esters (PET-OTs) were substituted with L-N-(trifluoroethyl)[4,5-H-3]lysinamide. On the other hand, direct coupling of PET-OH with heptafluorobutyl (p-isocyanatobenzoyl)[2-H-3]glycinate was performed; subsequent treatement with L-[4,5-H-3]lysine partially gave the ester substitution. All the samples were analyzed by liquid scintillation counting (LSC) and X-ray photoelectron spectroscopy (XPS). The ratios of derivatization recorded by LSC measurements, for membranes currently used as substrates in cell cultivation, were within 15-30 pmol/cm(2) of fixed amino acid labels. From XPS, we determined that 0.5-1% ofthe polymer units were derivatized in about 50 Angstrom depth. This study establishes practical conditions for the covalent anchorage of biologically active molecules on PET samples.