SummaryThe use of calf rennet substitutes in cheese manufacture will increase because of costs linked with the availability of calf vells on the world market and the development of new cheese making processes such as ultrafiltration. The development of recombinant DNA techniques for chymosin production will also have an impact on the traditional calf rennet market when rennet manufacture by this method has been perfected. Further research into the secondary action of rennet during cheese maturation will also lead to a better understanding of how rennet can influence the flavour and textural characteristics of various cheese.