Introduction In recent years ultrasound has found a number of important applications to biological problems. In particular, its destructive effects on the nervous system promise to be of experimental as well as practical value.1-4In appropriate dosage it may enhance or depress the functional activity of the central nervous system.5,6Little is known about these functional effects, which do not necessarily involve the production of detectable lesions. This study on peripheral nerve was undertaken to investigate the effects of focused ultrasound on axonal conduction in a mixed nerve, and to shed light on the nature of the central effects. Methods The sciatic nerves of large green frogs were used. The branches in the thigh were cut and the main trunk with its tibial and peroneal extensions, measuring about 7 cm. in length, was removed. Distally the tibial and peroneal branches were tied together. The nerve was mounted in