The total cytoplasmic ATP content (bound and free) increased in Escherichia coli when the bacteria were submitted to electric pulses with field strengths of 1-6 kV/cm and a decay time of 7-20 microseconds. The electron-transport chain was blocked by cyanide, and ATP synthesis was detected by a luminescence assay. The amount of newly formed ATP depends on the field strength. A total of 150 pmol of ATP was formed per milligram of bacteria submitted to a 3 kV/cm pulse. Synthesis was blocked by uncouplers and ionophores (valinomycin). The F1F0-ATP synthase inhibitor dicyclohexylcarbodiimide blocked a large part of this synthesis. Synthesis was not induced in unc mutants (unc B, unc D). The synthesis of ATP is related to the induced transmembrane potential, not to the Joule heating. A minimum 35-50-mV increase in membrane potential must be maintained for at least 12 microseconds to trigger this synthesis. This very fast energy transduction in bacteria is in good agreement with our previous results concerning submitochondrial particles. Because of the localized character of the induced membrane potential, these results are in agreement with the recent hypothesis of "mosaic proton coupling".