AbstractCrosslinked chloromethylated polystyrene beads were reacted with hydantoin and imidazolidinone derivatives to produce functionalized beads which could be rendered biocidal upon reaction with free chlorine or bromine. The biocidal efficacies of the N‐chlorinated, and in one case, the N‐brominated polymeric beads against Staphylococcus aureus and Escherichia coli O157:H7 in aqueous suspension have been determined. Synthetic methods and test data have been presented. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 368–372, 2004