A sterile, concentrated (100X) solution intended for use as one component in a complete culture environment for the growth of human mammary epithelial cells. Each 5 ml bottle of MEGS contains all of the growth factors, hormones, and tissue extracts necessary for the culture of mammary epithelial cells and is the correct amount of supplement for a 500 ml bottle of Medium 171. When a 500 ml bottle of medium is supplemented with MEGS, the final concentrations of the components in the supplemented medium are: Bovine pituitary extract (BPE) (0.4% v/v) Recombinant human insulin-like growth factor-I (1μg/ml) Hydrocortisone (0.5μg/ml) Human epidermal growth factor (3 ng/ml)