Serum is commonly used as a supplement to cell culture media. It provides a broad spectrum of macromolecules, carrier proteins for lipoid substances and trace elements, attachment and spreading factors, low molecular weight nutrients, and hormones and growth factors. The most widely used animal serum supplement is fetal bovine serum, FBS. Since serum in general is an ill-defined component in cell culture media, a number of chemically defined serum-free media formulations have been developed in the last two decades. Besides modern cell biological advances in cell and tissue culture and efforts towards a standardisation of cell culture protocols in Good Cell Culture Practice, in addition, considerable ethical concerns were raised recently about the harvest and collection of fetal bovine serum. Thus, in order to decrease the annual need for bovine fetuses in terms of the 3Rs through any reduction in the use or partial replacement of serum, as well as in terms of an improvement of cell and tissue culture methodology, serum-free cell culture represents a modern, valuable and scientifically well accepted alternative to the use of FBS in cell and tissue culture.