Pulse‐echo ultrasonic attenuation measurements were made for longitudinal and transverse waves in the [100], [110], and [111] propagation directions in NaCl specimens cut from a single boule. The attenuation &agr; was proportional to the orientation factor &OHgr; (relating the resolved stress on the slip system of the crystal to the applied stress), and to the square of the frequencyf. Under x‐ray irradiation, &agr; decreased for modes with &OHgr;=≠0 but remained constant where &OHgr;=0. Dislocation damping is considered to cause the loss.