Transient transfection of cell lines can be extremely useful in a number of applications. However, until recently, obtaining useful and reproducible percentages of transiently expressing DT40 was almost impossible. Standard techniques such as electroporation usually give low transfection efficiencies (can be up to 40%, but ususally less than 5%) while many liposome-based protocols result in the death of all cells. Recently Amaxa Biosystems GmbH (Cologne, Germany) have developed the 'nucleofector' system which has been shown to be effective in transfecting previously resistant cell lines. This system has, for the first time, allowed efficient and non-toxic transient transfection of DT40, routinely achieving transient transfection efficiencies of over 50%.