Two of the main reasons for developing serum-free medium are to improve the growth and to increase the productivity of a cell. This review has attetmpted to show that these goals can be achieved far more easily than generally realised by utilising the methods that have been developed during the past decade and by using a limited number of standard supplements. Serum-free media have contributed greatly to the advances made in recent years in the fields of cell biology and mammalian cell technology and it is clear that they will continue to play a major role in the clarification of cellular regulatory processes and in the refinement of processes in modern cyto-technology.