The F-12 Medium, also known as Ham’s F-12, was formulated by R. G. Ham (1965) for the synthetic, serum-free culturing of single-cell Chinese hamster ovary (CHO) cells. A key change over the predecessor medium F-10 is increased zinc, which greatly improved plating efficiency and reproducibility for CHO cells. F-12 was designed primarily for the plating of single cells and not for supporting populations exceeding 100,000 cells. However, it is now widely used for a variety of mammalian cell types. Depending on the type of culture, F-12 may require serum or protein supplementation.