This experimental investigation has demonstrated that an inflated pneumatic tourniquet causes slowing in conduction velocity of the sciatic nerve. The amount of slowing and recovery time vary according to inflation pressure and to the duration of applied pressure. The conduction velocity always returned to normal provided the tourniquet was inflated for 2 hours or less, and pressures were below 500 mm Hg. The nerve directly under the tourniquet was most susceptible to injury. Inflation pressure should be as low as possible and be determined according to systolic blood pressure. An Esmarch bandage should not be used as a pneumatic tourniquet because of its very small surface area. The cause of the nerve injury demonstrated is likely related to arterial ischemia.