HEPES (N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid) is a zwitterionic, organic buffer reagent that is often used in cell culture media to maintain the pH value of the cell culture medium. We offer HEPES as a solid and in solution. For our solution, HEPES was dissolved in water (cell culture quality) with a concentration of 1 M. HEPES buffers in a pH value range of 6.7 to 8.6. It is not membrane-permeable, has limited reactivity and is chemically and enzymatically stable. An addition of 10 to 25 mM HEPES to your cell culture medium therefore offers an alternative to sodium bicarbonate when cell cultures have to be cultivated without CO2 or an additional buffering capacity when stored outside a CO2 incubator for longer periods of time.