In mammalian cells, transfection frequency also increases dramatically, if DNA is co precipitated with calcium phosphate in the recipient cells. In all these methods, some of the transferred DNA, may integrate with the chromosomes of the cultured cells, thus resulting into stable transfection.

If the donor DNA encodes, a genetic trait, the recipient cells will express this trait. Transfection of cultured mammalian cells has been utilized extensively for detection of cancer genes (oncogenes) and for gene therapy experiments.

For detection and identification of a cancer gene, DNA from human tumour cell lines is purified, sheared into fragments (30-50kilobase pairs in length), dissolved in phosphate buffer and then precipitated by the addition of calcium chloride. The solution is poured onto a layer of mouse 3T3 cells, which develop foci of transformed cells.

These transformed cells can later be used for detection of cancer causing genes. (Mouse 3T3 cell lines are efficient for DNA uptake and have been used for decades to assay cancer causing genes).

Transfection of cultured cells has also been used for gene therapy, where the genes are inserted in cultured cells, which are then placed into the body of a patient for gene therapy.