The acoustic noise spectrum associated with the collapse of transient cavities produced by a stirring rod in water was measured in the frequency range 1–3500 kc. While the spectrum, in general, goes asf−2above 1 kc, flat regions are found between 20 kc and 100 kc, and again above 500 kc to at least 3500 kc. If the flat regions are due to discrete random impulses, two time constants,τ1≃10−6 secondandτ2<10−8 second, may be obtained by using the criterion 2πfτ≃1, wherefis the −3 db point beyond the flat region.With intense cavitation, the acoustic level fails off and becomes erratic in the 600‐kc region. Transmission measurements made through the cavitating volume show strong sound absorption, which appears to be caused by a cloud of small, stable bubbles.