To relieve deafferentation pain, electrophysiological assessment of target points was performed using deep cerebral SEPs. As a preliminary experiment, the relationship between the waveform of the SEP and the anatomical structure of the brain was examined in cats. The infraorbital nerve was stimulated and the SEP was recorede around the VPM. From the rostral edge of the medial leminiscus (ML), a high voltage positive wave was recorded, and from the ventral side of the VPM a wide negative wave with positive wavelets was recorded. For the treatment of three cases of thalamic pain, the deep cerebral SEP was recorded during the insertion of a chronic electrode for deep brain stimulation. By contralateral median nerve stimulation, the high voltage posotive waves (peak latency ; 13-15msec) from the ML and the subsequent unerven waves from the VPL were recorded along the trajectory. The later uneven waves were composed of wide negative waves and positive wavelets, which were thought to be derived from the synaptic activity of the VPL and thalamocortical rediation, respectively. Effective pain relief was obtained at the border zone of the ventral VPL and the ML, where the characteristic waves of the VPL changed to those of the ML. The deep cerebral SEP can be used for the identification of target points electrophysiologically.