Effects of phenytoin (PHT) on the intracellular calcium and intracellular protein changes during pentylenetetrazole (PTZ)-induced bursting activity in the neurons of the Japanese land snail Euhadra peliomphala were examined. In the examination with a computer controlled electron probe X-ray microanalyzer, PHT clearly inhibited the intracellular calcium shift induced by PTZ as well as the calcium binding state change near the cell membrane. PHT also clearly inhibited the intracellular protein changes induced by PTZ. PHT, however, did not show any change in the transmembrane ionic currents such as the sodium current, calcium current and potassium current. These findings suggest that one of the main sites of anticonvulsant action of PHT is pathologically changed intracellular calcium movement and intracellular protein changes during seizure discharge.