INTRODUCTION The subthalamic nucleus has been demonstrated to be involved in Parkinson's disease. Electrical stimulation of this nucleus at high frequency was proved to revert most symptoms and is used as the most advanced alternative therapy. The technique requires the recording of single cell activity as an important step in locating spatially the limits of the nucleus together with magnetic resonance imaging and ventriculography. OBJECTIVES To study the electrophysiological properties of single cells in the subthalamus. This information is important to recognize the nucleus in the operating room so as to implant the definitive stimulating electrode. PATIENTS AND METHODS Twelve patients with Parkinson's disease were implanted with bilateral electrodes in the subthalamic nucleus. Several neurological tests were applied during one year to study the clinical results. RESULTS Single cell activity was recorded in both hemispheres. Three types of cells were recognized based on the mode of discharge: tonic, phasic and rhythmic. The track chosen to implant the definitive electrode was based on the higher number of cells recorded and on the response to tremor and passive or voluntary movements. The neurological tests applied demonstrated a diminution of the symptoms. CONCLUSION The subthalamic nucleus plays an important role in handling motor and sensory information. Stimulation of the nucleus at high frequency reveals an amelioration of Parkinson's symptoms during the one year period of study.