Deep brain stimulation of the subthalamic nucleus (STN) is becoming the procedure of choice to reduce symptoms of Parkinson's disease such as rigidity, akinesia and tremor. We present here a series of electrophysiological recordings performed in 34 patients along a standardized electrode trajectory. Neuronal activity along the trajectory consists of a first heterogeneous population of thalamic cells with a mean frequency of 24.8+/-1.4 Hz followed by a silent zone and a second population of STN neurones with a significantly higher spiking frequency (P<0.001) of 42.3+/-1.8 Hz. This study confirms previous findings and suggests that rapid measurement of neuronal spiking frequency and burst index is sufficient to determine precisely the vertical position of the STN.