The denaturation of enzymes in solution by cavitating ultrasound has been reported previously. This report presents the results of an extensive study of the effects of noncavitating ultrasound on solutions of α‐chymotrypsin, trypsin, aldolase, lactate dehydrogenase, and ribonuclease. In one set of experiments, the solutions were irradiated and then analyzed to determine the effects on the physical and chemical properties of the enzyme molecules. Irradiations were carried out at different pH values and temperatures using 1‐MHz ultrasound at an intensity of 75 W/cm2, 10‐min continuous exposure, and 11‐MHz ultrasound at an intensity of 1000 W/cm2, 2000 0.1‐sec pulses. Analytical procedures employed included measurements of enzyme activity, specific optical rotation, uv absorption spectrum, and sedimentation coefficient. In a second set of experiments, enzyme‐catalyzed reactions were irradiated with ultrasound and simultaneously monitored spectrophotometrically. Ultrasound in the intensity range 0.5–35 W/cm2 at the frequencies 1, 9, and 27 MHz were employed with the temperature and pH held constant. Comparison of the results of this study with those from studies employing cavitation shows that cavitation is a necessary condition for ultrasonic denaturation of the five enzymes of this study.