Although cells that are chemically efficient are simpler and easier to use, the one drawback with these cells is their inefficiency at taking up larger plasmids. Using electro-competent cells may be the best way to work around this drawback when you want to transform large plasmids. This involves applying an electro-magnetic field to the cell/DNA mixture to improve membrane permeability. When you need to transform large plasmids, this technique works better than using heat-shock to cause the cells to take up the DNA. You will need access to an electroporator and the appropriate cuvettes to implement this technique.