Specular reflection of ultrasonic waves by a flaw plane is affected by the degree of contact of the flaw-plane faces. In general terms, a flaw plane may be viewed as a region where separation zones and contact zones can both exist, and friction may be significant over the contact zones. Achenbach and Norris1 have proposed a set of nonlinear flaw-plane conditions to account for the separation and friction effects. Other conditions, of a linear type, have been discussed by Thompson and Fiedler2.