Minimum Essential Medium (MEM) is a common cell culture medium developed from early work using Basal Medium Eagle (BME) with normal mammalian fibroblasts and certain subtypes of HeLa cells. This research indicated that additions made to BME aided cell propagation. MEM is modified with higher concentrations of amino acids to more closely approximate the protein composition of mammalian cells. When supplemented with serum, MEM has been used for cultivation of a wide variety of cells grown in monolayers, such as fibroblasts.