A simple physical chemical method of transferring genes into eucaryotic cells is described. Electric impulses in the intensity range of 5–10 kV/cm with a duration of 5–10 [mu]s were found to appreciably increase the uptake of DNA into cells. After electric field treatment, stable transformants were obtained in a system containing mouse cells deficient in thymidine kinase and a plasmid DNA harbouring the Herpes simplex thymidine kinase gene. The efficiency of transformation well compares with the results of biochemical methods of gene transfer. The electric field technique appears unique in its ease and simplicity.