The effects of lidocaine on repetitive firing of the CA1 pyramidal cells were studied in the hippocampal slice preparation using conventional intracellular recording technique. The cells were activated by injecting depolarizing current through the recording microelectrode. Lidocaine (50 μM) diminished the repetitive firing and progressively reduced the maximal rate of rise of the successive action potentials. The firing produced by low currents was little affected but that produced by high currents was substantially depressed. The maximal rate of rise of successive action potentials produced by a train of short depolarizing pulses was also progressively reduced, especially at high frequency (100 Hz) of activation. These findings suggest that, in the hippocampal pyramidal cells, lidocaine causes a use-dependent depression of the Na+ current. This action may be responsible for the anticonvulsant effects of lidocaine since it occurred at a clinically relevant concentration.