To provide further information on dry sliding wear and the accompanying metal transfer, wear experiments of radioactive brass rings against hardened steel have been conducted in a ring tester. The effect on metal transfer of sliding speed, surface finish, material of the harder surface, and the presence of slots in the steel ring have been investigated. Tests have also been conducted in argon atmospheres to exclude oxidation. Wear of brass on brass has been investigated by using radioactive rings against inactive rings. Results indicate a complex wear mechanism in which transfer, back transfer, and removal of transferred material are intermediate steps, and in which the determining step in wear rate is governed by the geometry of the rings rather than the apparent area of contact.