The object of the study was to investigate the sound field existing close to a plate that was free to vibrate and was exposed to an incident‐sound field. Modification of the sound field was sought other than that due to diffraction. This would occur when sound is reradiated under conditions of plate resonance. A square, galvanized, aluminum plate, 12×12×0.020 in., clamped along all four edges, was selected for the study. A simple mode of vibration of the plate, for which a single nodal circle was observed, occurred at a frequency of 74 cps. The amplitude and phase of vibration of the plate relative to progressive plane wave excitation was determined at frequencies in the region of this plate resonance. Simultaneously the acoustic field both adjacent to and distant from the plate's surface was determined. Significant modifications to the incident sound field, as large as 10 dB, were observed. An analysis was developed that, given knowledge of the plate's vibration, accurately predicted this sound‐field modification. [This study was supported in part by the U. S. Air Force.]