High efficiency gene transfer into mammalian fibroblasts is a routine procedure that can be performed by a variety of methods (1), but transfection of epithelial cells has been more difficult to achieve. Each of the standard techniques has associated problems; special equipment is required for electroporation (2) and also for direct microinjection (3). Protoplast fusion (4) is suitable only for cloned genes. Retroviral transduction of genes (5) is a method of high efficiency for animal cells, but again is applicable only to cloned genes of restricted size, and safety considerations are likely to restrict greatly the use of retroviral vectors suitable for human cells. Calcium phosphate coprecipitation has been used with success in several epithelial lines (6,7,8) and, more recently, strontium phosphate coprecipitation (9). These techniques are very simple to perform, require no special equipment, and can be applied to genomic DNA transfection.