Serum-free medium is routinely used as an alternative to standard serum-containing media because it offers multiple advantages. Its composition is better defined. Uncontrolled variables commonly associated with serum-supplemented media, such as indeterminate levels of vitamins, hormones, and growth factors, are eliminated, and the potential for contamination by infectious agents is reduced. In addition, serum-free media offers researchers the ability to specifically design their media for a particular cell type. R&D Systems offers multiple serum-free, chemically defined, concentrated media supplements designed for culturing neurons and neural stem cells.