1. Remove and discard culture medium.
2. Briefly rinse the cell layer with Ca++/Mg++ free Dulbeccos phosphate-buffered saline (D-PBS) or 0.25% (w/v) Trypsin- 0.53 mM EDTA solution to remove all traces of serum which contains trypsin inhibitor.
3. Add 2.0 to 3.0 mL of Trypsin-EDTA solution to flask and observe cells under an inverted microscope until cell layer is dispersed (usually within 5 to 15 minutes)xa0Note: To avoid clumping do not agitate the cells by hitting or shaking the flask while waiting for the cells to detach.xa0 Cells that are difficult to detach may be placed at 37°C to facilitate dispersal.
4. Add 6.0 to 8.0 mL of complete growth medium and aspirate cells by gently pipetting.xa0
5. Add appropriate aliquots of the cell suspension to new culture vessels.
6. Incubate cultures at 37°C.

NCI-Navy Medical Oncology Branch Cell Line Supplement. J. Cell. Biochem. suppl. 24: 1996.

Freshney RI. Culture of Animal Cells: A Manual of Basic Technique, 5th edition. New York: Wiley Liss; 2005. For more information on enzymatic dissociation and subculturing of cell lines see Chapter 13.