In 1962, R. G. Ham developed a medium for supporting single-cell growth of a diploid Chinese hamster ovary (CHO) cell line, a formulation now known as Ham’s F-10. This medium was found to be superior to an existing medium, F7, for both serum-free growth of CHO and for low-serum requirements of other mammalian cell lines. The key features include a higher amount of arginine, low tryptophan, proline and a variety of other nutrients such as thiamine, hypoxanthine and zinc. Depending on the application, commercial formulations of Ham’s F-10 may come with or without serum supplementation.