Developments in the molecular genetics of food bacteria have now made possible the construction of designer cultures with the potential to improve important characteristics of cheese including production efficiency, safety and health properties. Such advances are set to expand the range and understanding of both starter and probiotic cultures, especially at a time when the total genomes of many strains are being determined and will become available. To illustrate the types of improvements which such technologies can bring, examples are given such as development of bacteriophage resistant starters and bacteriocin-producing starters with the potential to control adventitious cheese flora. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.