Abstract: Electroporation of mammalian cells is performed to high efficiency by use of a buffer solution containing trehalose, sucrose, or both, in addition to an inorganic phosphate buffer, an organic sulfonic acid buffer, a halide salt of an alkali or alkaline earth metal, a chelating agent, an alkyl methyl sulfoxide, and a nucleotide triphosphate, with substantially no sodium. This buffer solution is effective both in the electroporation of cells that are suspended in the buffer solution and in the electroporation of cells that are fixed on a surface.