It is known that a gas bubble pulsating in a sound field in a liquid containing dissolved gas can grow by a process called “rectified diffusion.” If the liquid is undersaturated with the gas at the existing static pressure, growth of the bubble will occur only if the sound pressure exceeds a threshold value. The threshold sound pressure for growth by rectified diffusion has been measured for individual air bubbles trapped at the center of a water-filled sphere resonating at a sound frequency of about 25 kc/sec. The data cover a range of bubble sizes, static pressures, and air contents of the water. The measured thresholds are several times larger than Blake's theoretical values (Acoust. Research Lab. Harvard Univ. Tech. Memo. 12, September, 1949) or values calculated from several refinements of the theory.