The subject of sliding friction is of great technological importance and has been studied extensively on an engineering basis, but many of the underlying microscopic factors that control friction or wear remain obscure. The present study is part of an effort to relate sliding deformation to the crystal structure of the contacting surfaces. The method was to scratch a steel ball in various crystal directions on an accurately finished surface of Cu-Al single crystals. For a scratch on the (111) face, the scratched track width and the width of the slipped area were found to be wider in the [211BAR] direction than in the [211BAR]. The mechanism of the active slip produced by the scratch can be explained in terms of stress patterns and interactions among the dislocations produced in the subsurface region. The distributions of dislocation density on the cross-section perpendicular to the (111) face were elucidated.