1. Remove media from wells or a tissue culture flask.
2. Add 1X chilled freezing medium to the cells.
1X freezing medium (I): 7%-10% DMSO in growth medium with 10% FCS and without antibiotics
1X freezing medium (II): 7%-10% glycerol in growth medium with 10% FCS without antibiotics
3. Place plates or flasks in a prechilled styrofoam container (-70 °C) and close off completely.
Place in -70 °C freezer. Cells can be stored at -70 °C for months.