In metallic alloys the stress-induced reorientation of solute pairs produces an anelastic relaxation called the Zener effect. To determine whether or not this relaxation is also observable in a nonmetallic solid solution, internal friction of single crystals of NaCl plus (1.3% to 1.7%) KCl is measured at 4 to 10 kc/sec. A maximum in the damping occurs near 400°C for nominally pure NaCl:KCl and near 300°C for NaCl:KCl crystals with CaCl2 added to enhance the cation vacancy concentration. This behavior indicates that the Zener relaxation is present in NaCl:KCl. Diffusion constants calculated from this Zener relaxation agree well with the results of radioisotope diffusion experiments. © 1965 The American Institute of Physics.