Measurements of high-altitude pressure waves from underground and surface explosions are of interest, as these waves can affect ionospheric electron density and be a source of infrasonic signals. Canisters, equipped with parachutes, were dropped from aircraft to determine time histories of pressure waves radiated by the ground surface above an underground nuclear explosion and a surface chemical explosion. These canisters contained transducers to document pressure and acceleration histories as well as a transmitter to relay information to ground receiver stations. We found observed pressure histories from the underground explosion to be consistent with histories calculated from surface ground motion records. The peak blast wave overpressures from the chemical explosion agreed with predicted scaled values. Observed time histories, however, had shorter positive phase duration than predicted with scaling. ¿1991 American Geophysical Union