Developed by Ham, nutrient mixture Ham's F-12 has higher levels of amino acids, vitamins and trace elements. Putrescine and linoleic acid were added to the formulation. The medium was originally designed for the serum free growth of Chinese hamster ovary and lung cells. When used with whole or dialyzed serum or in combination with hormones and transferrin, Ham's F-12 is widely used to grow a broad spectrum of mammalian and hybridoma cells. Ham's F-12 today is the medium of choice for clonal toxicity-assays using CHO cells (CHD-3 and CHL-1). For optimum buffering, use in a 5% COs atmosphere.