Human Mammary Epithelial Cell Basal Medium (formerly ''Medium 171'') is a sterile, liquid tissue culture medium intended for use in a complete culture environment for the growth of normal human mammary epithelial cells. This medium contains essential and non-essential amino acids, vitamins, other organic compounds, trace minerals, and inorganic salts. It does not contain antibiotics, antimycotics, hormones, growth factors, or proteins. It is HEPES and bicarbonate buffered and designed for use in an incubator with an atmosphere of 5% CO₂/95% air.

To support plating and long-term proliferation of normal human mammary epithelial cells, Human Mammary Epithelial Cell Basal Medium must be supplemented with Mammary Epithelial Growth Supplement (MEGS) (Cat. No. S0155). Each 5-mL bottle of MEGS contains all of the growth factors, hormones, and tissue extracts necessary for the culture of normal human mammary epithelial cells and is the correct amount of supplement for a 500 mL bottle of Human Mammary Epithelial Cell Basal Medium.

When a 500 mL bottle of medium is supplemented with MEGS, the final concentrations of the MEGS components in the supplemented medium are: BPE, 0.4% v/v; recombinant human insulin-like growth factor-I, 0.01 μg/mL; hydrocortisone, 0.5 μg/mL; and recombinant human epidermal growth factor, 3 ng/mL.