Icebergs seem to have escaped serious attention as sources of underwater sound. The noise of icebergs has been measured by means of sonobuoys dropped by an aircraft at distances between 200 and 10 000 yd. Two isolated icebergs 130 to 150 ft high were measured at a location northeast of Newfoundland. Noise apparently originated by the bergs was found to have a spectrum flat to about 10 kHz, the limit of measurement, with spectrum levels of −37 and −42 dBre1 dyn/cm2at 200 yd from the two bergs. Ice sizzle is readily observed with a cube of cloudy ice and a hydrophone in a container of water. It is surmised that this noise is caused by the explosion of tiny air bubbles entrapped in the ice under pressure and released as melting occurs. Alternatively, at deep depths, the process may be one of implosion of the cavities by inrushing water. The level of the noise of icebergs doubtless depends on many factors, such as size, depth, air content, and rate of melting in the surrounding water.