AbstractA relatively simple, autoclavable medium was developed that would support the growth of the mouse fibroblast (MFL) cell line in suspension culture. This medium was prepared in three stages with decreasing quantities of serum. As the serum was reduced from 5% to none, the amount of Bacto‐Peptone was increased from none to 0.5%. The reduction and finally elimination of serum did not affect proliferation adversely, but actually seemed to produce more rapid growth and higher levels of cell populatio