Continuous culturing of cell lines can be potentially prone to cross contamination and genetic drifting. During experimentation, the cell lines have limited quantity and the laboratory equipment may fail, that's why cell freezing is a practical way to save time and expenses.

The best way to preserve these cell lines for a long time is to cryopreserve it. It is by using liquid nitrogen with a cryoprotective agent like dimethylsulfoxide to be placed in a cryovial. Dimethylsulfoxide can reduce the freezing point of the medium, thus allowing for a slower cooling rate, which reduces occurrence of ice crystal formation that can damage the cell that cause cell death.

To cryopreserve a cultured cell, one must first prepare a freezing medium. It is to be stored at 2°-8°C until it is ready to be used. The quantity and viability of the cells are then measured using a hemacytometer, cell counter and Trypan Blue. This can calculate the required volume of the freezing medium. After, centrifuge the cell suspension and decant the supernatant leaving the cell pellet intact. The cell pellet then shall be resuspended in a cold freezing medium at the recommended viable cell density. The aliquots of the cell suspension will be placed in cryovials.  In a controlled  rate, freeze the cells decreasing the temperature to 1°C approximately. Or, the cryovials can be placed in an isopropanol chamber to be stored at -80°C. Lastly, the cells shall be transferred to a liquid nitrogen medium to be stored at its vapour phase.

To perform the method with best results, the cultured cells must be freezed at a high concentration with the possible lowest passage. The cells should also be 90% viable before freezing. The frozen cells must be stored below -70°C as cells deteriorate at -50°C. Also, the cryovials must be sterile and use proper aseptic technique to ensure the sterility of the procedure. A recommended freezing medium should be used containing a cryoprotective agent such as dimethylsulfoxide or glycerol.

Always remember that the specimen must always be stored in the vapour phase as this can decrease the risk of explosion. If the liquid phase of liquid nitrogen must be used, use a cryovial that is specifically used for the liquid phase and always be cautious with the risk of explosion. Above all, always wear protective clothing such as a long laboratory gown, face shield or goggles, long pants, cryogenic gloves and closed toe shoes.