Studies have been conducted to test the effect of Ginseng alcohol extract on the membrane potentials of frog skeletal muscle. The gastrocnemius muscle was isolated and placed in a chamber containing the Clark-frog Ringer solution. Membrane potentials were recorded using microelectrodes filled with 3 M KCI and muscle was electrically stimulated to obtain action potential. Changes in both the action potential and the resting membrane potential were observed after adding an appropriate amount of Ginseng alcohol extract in the perfusing Ringer solution. The results obtained from 346 muscle cells are summarized as follows : 1) The average resting membrane potential of the normal frog gastrocnemius muscle cell was -92.8 mV and the peak of the action potential reached at 29.8 mV. 2) Both the resting membrane potential and the peak of the action potential decreased by Ginseng alcohol extract, the effect being proportional to the dose of Ginseng alcohol extract. 3) The resting membrane potential and the peak of the action potential continuously decreased until about 40 min after Ginseng addition and leveled off thereafter. The potentials recovered to its original value after Ginseng was washed out. 4) The resting membrane potential was more sensitive to the Ginseng alcohol extract than was the action potential. These results strongly suggest that Ginseng alcohol extract increases both the Na⁺ and K⁺ permeability in the skeletal muscle cell membrane.