CMRL Medium, which may refer to CMRL 1066 or CMRL 1415, is a chemically defined medium developed by Healy and others in 1955. It was first used to grow mouse Earle’s strain L cells, which had been shown to proliferate continuously for over 10 years without protein supplementation. The recipe features nucleotides, glutathione, and glucose, among other constituents. CMRL medium is suitable for culturing in both serum and serum-free conditions. Commercial formulations of CMRL medium may contain phenol red, glutamine, or supplementation.