Biocidal compositions comprises an effective amount of a biocidal agent such as a quaternary ammonium compound or a blend of quaternary ammonium compounds and an effective amount of a cellular membrane disruptor. The synergy index of the biocidal agent and the cellular membrane disruptor is less than 1. The biocidal compositions can further comprise an effective amount of a chemical stabilizer and other optional components such as a nonionic surfactant. Methods for making and utilizing such biocidal compositions are also disclosed.
