Calcium phosphate forms an insoluble precipitate with DNA, which attaches to the cell surface and is taken into the cells by endocytosis. The protocol is easily adapted for use with other types of cells, both adherent and nonadherent. This protocol is a modified version of a method published by Jordan et al. (1996) who rigorously optimized calcium-phosphate-based transfection methods for Chinese hamster ovary cells and the 293 line of human embryonic kidney cells. - [Read Calcium-phosphate-mediated Transfection of Eukaryotic Cells with Plasmid DNAs]