The effect of ultrasound at various energy levels on the conduction properties of neural tissue is explored in this in vitro study. Excised sciatic nerves from the bullfrog were used for experiments. The nerves were stimulated by 3.5 MHz continuous wave ultrasound at 1, 2, and 3 W for 5 min. The peak-to-peak amplitude of the electrically evoked compound action potential (CAP) and the conduction velocity (CV) were measured in the nerves before and during ultrasound stimulation. The CV of the nerves increased by 5-20% for ultrasound stimulations at 1-3 W. The CAP amplitude increased by 8% during stimulation with 1 W ultrasound, and progressively decreased for 2 and 3 W ultrasound. This indicates that the effect of lower energy ultrasound increases both the CV and the CAP amplitude and that the reduction in the CAP amplitude for higher energy ultrasound is associated largely with ultrasonic thermal effects.