In HIFU applications to ultrasound surgery, it is important to intensify acoustic energy absorption in the focal region without increase of heating in the prefocal region. This regime may be achieved by using the mechanism of nonlinear absorption, which is more pronounced when sharp shocks are developed in the waveform. In this report, results of an experimental study of nonlinear enhancement of ultrasound heating induced by a sawtooth wave are presented. A focused beam was radiated from a 1 MHz piezoceramic transducer with 10 cm diameter and 20 cm focal length. The wave was focused through water into a gelatin sample with a thermocouple implanted near the focal point of the beam. The transducer was excited by repetitive tone bursts. Cases with various amplitude and duration of the tone burst but with the same level of mean power were compared. It was shown that the heating was more efficient for higher amplitudes when shock fronts were formed at the focus. ©2000 American Institute of Physics.