Cell Systems Complete Classic Medium (4Z0-500) is recommended for the growth phase of cells. Once the culture is established, you can switch to Serum-Free Medium (SF-4Z0-500) supplemented with CultureBoost-R, if your experiments require the absence of serum. Alternatively, you may culture the cells exclusively in Serum-Free Medium (SF-4Z0-500) supplemented with CultureBoost-R, if the cells are plated and maintained at a high cell density. For example, instead of seeding the contents of 1 vial of cells into a T75 flask per our standard protocol, seed the contents of 1 vial of cells into 2 x T25 flasks in Serum-Free Medium supplemented with CultureBoost-R. Note that the cells will not grow as quickly as in Complete Classic Medium (4Z0-500).Note that Serum-Free Medium (SF-4Z0-500) is a chemically defined complete medium, distinct from Media Minus Serum (4Z3-500).