Light scattering by crystals of potassium chloride grown at the Harshaw Chemical Company and at theNaval Research Laboratory was measured. Scattering by the Harshaw crystals varies with crystal orientationwhile scattering from the NRL crystals does not. The major part of the Harshaw crystal scattering isattributed to vacancy-impurity clouds around dislocations which have the scattering pattern of cylinderswith5×105 Ålength, radius 100–500 Å, and axis parallel to (100) directions. The major part of the NRLcrystal scattering is attributed to impurity precipitates which have the scattering pattern of spheres 1400–1600Å in diameter. Air quenching of the crystals to room temperature from temperatures up to 650°Cproduced marked changes in the scattering. The results of the quench treatments are tentatively interpretedin terms of the migration of defects.