A high performance Stark cell has been made of which the essential features are stainless steel plates, 2-mm spacing, electric fields up to 100 kV/cm, field uniformity better than 5*10/sup -5/. This Stark cell has been placed at a waist created inside a CO/sub 2/ laser cavity, so that the beam propagates almost freely inside the cell. Thus one obtains the high sensitivity of intracavity spectroscopy but preserves the quality and the stability of extracavity spectroscopy.