It is known that transient cavities, generated by cavitation in an acoustic stationary wave, travel at high velocities outward from the region of high acoustic pressure. An analysis of the motion of these cavities generated in a cylindrical resonator has been made. Cavity velocities, on the order of 100 cm/sec, were obtained by photographing the cavitation event under stroboscopic illumination. Owing to the short duration of the stroboscopic flash, considerable detail can be seen in the photographs of individual cavities moving outward from the acoustic pressure antinode. Acoustic pressure amplitudes were near but above threshold and varied from approximately 3 to 8 bars. The cavities varied in size, were roughly spherical in shape, and tended to break up as they collapsed. Some photographs show several tracks diverging from the same point, apparently originating simultaneously. It is found that if the cavities are treated as spherical bubbles, then the observed motion agrees roughly with that predicted analytically. [Work supported by the Office of Naval Research and the Naval Academy Research Council.]