Minimum Essential Medium (MEM was, developed by Harry Eagle. It is one of the most widely used of all synthetic cell culture media. Early attempts to cultivate normal mammalian fibroblasts and certain subtypes of HeLa cells revealed that these types of cells had specific nutritional requirements that could not be met by Eagle's Basal Medium (BME). Studies using these and other cells in culture indicated that additions to BME could be made to aid growth of a wider variety of fastidious cells. MEM incorporates these modifications which includes higher concentrations of amino acids so that the medium more closely approximates the protein composition of mammalian cells. MEM has been used for cultivation of a wide variety of cells grown in monolayers. Optional supplementation of non-essential amino acids to the formulations that incorporate either Hanks' or Eagles' salts has broadened the usefulness of this medium.