The preparation of an antimicrobial nylon material and its properties are discussed. Biocidal cyclic N-chloramine moieties were covalently bonded to Nylon 66. These moieties, which included hydantoins, oxazolidinones, and imidazolidinones, were stable during at least 3 months of dry storage, and their antimicrobial activities, once lost by reaction with reducing sodium thiosulfate, could be regenerated by exposure to free chlorine. Biocidal swatch tests showed that the nylon fabrics containing N-chlorinated hydantoin functional groups provided a 7.2 log reduction of Staphylococcus aureus and a 7.1 log reduction of Escherichia coli at a contact time of only 10 min. Antimicrobial nylon should find a variety of important uses such as in clothing, carpets, sutures, brushes, and so forth.