Abstract In microsurgery of the middle ear using argon laser, heat is produced on the sensorineural structures adjacent to the irradiated bones.

Thermal gradients following laser applications have been measured by means of special thermocouples.

The footplate was perforated by a 50 msec. ray applied both at 380 m Watt and at 460 m Watt. The maximum temperature increase registered in the labyrinthine spaces was respectively 2oc. and 3.5oC.

Coagulation of the promontory mucosa was performed using 100 msec. impulses at 200 m Watt. At the end of a series of 12 applications the temperature increase at the level of the basal coil was 1.4oc.

From the above results the authors conclude the no damage is induced during laser microsurgery and that, considering the power and time values relative to impulses, the use of laser in routine clinical practice should be relatively safe.