Minimum Essential Medium (MEM) with Earle’s Balanced Salts was developed by Harry Eagle as a result of his studies to determine the essential nutritional requirements of mouse L cells and HeLa cells in culture. He demonstrated that these cells require 13 amino acids and 7 vitamins to grow and reproduce in vitro. MEM is a modification of Eagle’s earlier medium Basal Medium Eagle (BME), containing higher concentrations of the essential nutrients. This medium has demonstrated the ability to support a variety of normal and transformed cells in culture and contains Earle’s Balanced Salts, which makes it suitable for use in atmospheres charged with CO2 gas. Minimum Essential Medium Joklik’s Modification (JMEM) was designed for suspension culture systems. Calcium chloride has been omitted to reduce cellular attachment.