Surface carboxylated PEEK films were obtained from a common key-intermediate, the PEEK-OH film, resulting from the surface reduction of amorphous PEEK film. Substitution of the hydroxyl groups, under mild acidic conditions, with 4-aminobenzoic acid and succinamic acid gave PEEK-Ph-CO2H and PEEK-(CH2)(2)-CO2H in 38% and 70% yields, respectively. The sample surfaces were analysed by X-ray photoelectron spectroscopy. The reactivity of PEEK-(CH2)(2)-CO2H was assayed by activation with WSC, SOCl2 or CDI, followed by coupling to H-3-lysine and liquid scintillation counting of the radioactivity associated with the samples.