Polyamide fibers were modified for the attainment of antibacterial activity using a graft copolymerization method. The fibers were grafted with monomers containing quaternary ammonium groups using sodium persulfate as initiator. Two monomers were used as vinyl monomers. The first monomer, called METAC, is methacryloyloxyethyl trimethylammonium chloride [H2C = C(CH3)CO2CH2CH2N(CH3)(3)Cl]. The second monomer, denoted CATAL, is a methacryloyloxyethyl dimethyldodecylammonium bromide [H2C = C(CH3)CONHCH2CH2CH2N(CH3)(2)(C12H25)Br], kindly supplied by Catalyze (France). The graft copolymerization was confirmed by several methods such as elemental analysis and FTIR spectroscopy. The antibacterial activity of modified samples was investigated against Staphylococcus aureus using the antibacterial standard AFNOR test method XP G39-100. Polyamide fibers grafted with the second monomer exhibit high antibacterial activity against S. aureus, but the fibers grafted with the methacryloyloxyethyl trimethylammonium chloride did not. (c) 2005 Wiley Periodicals, Inc.