Polytetrafluoroethylene (PTFE) treated with the cationic surfactant, tridodecylmethylammonium chloride (TDMAC), binds 14C-penicillin (1.5-2 mg antibiotic/cm graft), whereas untreated PTFE or PTFE treated with anionic detergents shows little binding of antibiotic. TDMAC-treated PTFE concomitantly binds penicillin and heparin, generating a surface that potentially can resist infection and thrombosis. The retention of these biologically active molecules is not due to passive entrapment in the PTFE but reflects an ionic interaction between the anionic ligands and surface-bound TDMAC. Penicillin bound to PTFE is not removed by exhaustive washing in aqueous buffers but is slowly released in the presence of plasma or when the PTFE is placed in a muscle pouch in the rat. Muscle tissue adjacent to the treated PTFE shows elevated levels of antibiotic following implantation. PTFE treated with TDMAC and placed in a muscle pouch binds 14C-penicillin when it is locally irrigated with antibiotic or when penicillin is administered i.v. The TDMAC surface treated in vitro or in vivo with penicillin provides an effective in situ source for the timed release of antibiotic.