Leibovitz's L-15 is CO2-independent. It buffers using free base amino acids and phosphate instead of sodium bicarbonate, and uses galactose rather than glucose so less lactic acid is produced. That lets it hold pH in ambient air in a sealed vessel, which is why it is used for insect and fish culture and for tissue transport. It should not be used in a CO2 incubator, where it will acidify.
Leibovitz’s L-15 Medium is a widely used medium with one defining feature: it holds the correct pH without a CO2 incubator. Developed by Albert Leibovitz, L-15 is buffered in a way that lets cells be cultured or handled in ordinary air, which makes it valuable for work outside the incubator. This guide explains what L-15 is, how its buffering works, what it contains, and which cells it suits.
Key Facts
- Type: CO2-independent basal medium
- Buffering: No bicarbonate; amino acids + galactose (works in air)
- Best for: Culture and transport without CO2
- Supplement: ~10% FBS + L-glutamine
What is L-15 medium?
L-15 is a chemically balanced basal medium designed for CO2-independent culture. Instead of relying on a sodium bicarbonate buffer, which needs a CO2 atmosphere to work, L-15 maintains pH through a combination of free-base amino acids, galactose, and sodium pyruvate. As a result, it keeps a stable pH in ambient air, so cells do not need a CO2 incubator. Like other basal media, it is completed with serum and glutamine before use.
How L-15’s buffering works
Most basal media use a bicarbonate buffer and must be kept in a CO2 incubator, because the CO2 in the air balances the bicarbonate to hold the right pH. L-15 replaces that system: it substitutes galactose and sodium pyruvate for glucose as energy sources, which reduces acid buildup, and uses higher levels of certain amino acids to buffer the medium. This is why L-15 is often called a CO2-independent medium.
What is L-15 used for?
L-15 is especially useful when cells must be handled outside a CO2 incubator, including:
- Cell culture and transport without a CO2 supply
- Primary cultures and cell lines that tolerate or prefer CO2-independent conditions
- Certain insect and cold-blooded animal cells, and tissue or organ culture handled in air
What is in L-15?
A typical L-15 formulation contains inorganic salts, a broad set of amino acids (some at raised levels for buffering), vitamins, galactose and sodium pyruvate in place of glucose, and phenol red as a pH indicator. Notably, it contains no sodium bicarbonate buffer, which is what allows it to work in ambient air.
How to supplement and use L-15
Before use, L-15 is completed with serum (commonly 10% FBS) and L-glutamine or a stable glutamine dipeptide. Because it is CO2-independent, keep cultures in a sealed or tightly closed vessel in a non-CO2 incubator or at the appropriate temperature in air. Store it refrigerated and protected from light, warm it gently before use, and keep the same lot across an experiment for consistency.
Working outside a CO2 incubator? See our guide on why L-15 is CO2-independent and the mistakes that cost viability.
Which L-15 do you need?
Browse all L-15 media · all cell culture media
Made in the USA and manufactured in house. Certificate of Analysis with every lot. Bulk pricing, purchase orders and custom formulations welcome.
