A study to determine the feasibility of measurement of conduction velocities through the lumbosacral nerve roots by direct percutaneous stimulation of the cauda equina is reported. The technique was applied to a series of normal volunteers and its reliability and reproducibility confirmed. An electrophysiologic defect was demonstrated in most patients with surgically proven lateral recess stenosis. Electrophysiologic recovery was shown in patients examined after surgery, Although the technique can be refined, these early results are encouraging.