An apparatus has been assembled for the study of sonically induced cavitation in the frequency range of 20 to 40 kilocycles. Radially symmetric standing waves are produced in a spherical resonator driven externally by a magnetostriction transducer. The acoustic pressure within the sphere is measured by a small barium-titanate transducer positioned at secondary maxima of the standing pressure wave. Equipment is provided for measuring the gas content of the liquid being studied. Measurements of cavitation thresholds as functions of air content, hydrostatic pressure, temperature, and surface tension have been made using different liquids. The highest thresholds measured were 200 bars for water and 140 bars for benzine (petroleum ether). The air content of the liquid appears to be the dominant factor limiting the maximal negative pressure which the liquid can withstand as long as the air content is greater than five percent of saturation. At lower percentages of air saturation the threshold becomes essentially independent of air content, becoming limited by as yet undetermined factors.