In 1973, Graham and Van der Eb serendipitously discovered that when DNA dissolved with calcium chloride is slowly added to media with phosphate, the DNA co-precipitates with calcium phosphate. This precipitation causes DNA to be more easily adsorbed to the cells, allowing for effective transfection. This method has since become routinely used for transfection of cell and tissue cultures to produce stable transformants. Several commercial kits utilizing the calcium phosphate method have been developed and optimized for ease of use and high transfection efficiency. Some reported tips for improving transfection in certain cells include glycerol or DMSO shock, and using a BES-buffered system.