When applying ultrasonics to the labyrinth for destructive purposes it is necessary to observe the following points: (1) liquid coupling of the treatment rod to the bone must be provided; (2) the bone over the external semicircular canal must be flattened and reduced in thickness to 1/2–1/4 mm; (3) the treatment rod and bone must be cooled to avoid thermal damage to the facial nerve; (4) the transducer must be maintained correctly in tune to avoid loss of ultrasonic output and the development of excessive side-lobes which might endanger the facial nerve or cochlea.