The choice of medium depends mainly on the type of cells to be cultured (normal, immortalized or transformed), and the objective of culture (growth, survival, differentiation, production of desired proteins).

Nontransformed or normal cells (finite life span) and primary cultures from healthy tissues require defined quantities of proteins, growth factors and hormones even in the best media developed so far. But immortalized cells (spontaneously or by transfection with viral sequences) produce most of these factors, but may still need some of the growth factors present in the serum.

In contrast, transformed cells (autonomous growth control and malignant properties) synthesize their own growth factors; in fact, addition of growth factors may even be detrimental in such cases. But even these cultures may require factors like insulin, transferrin, silenite, lipids, etc.