Steel (AISI-304) disks, polished to a 3 μm diamond finish, were implanted to doses of about 2 × 1017/cm2 with N+, Ni+ or, Ne+, ions. Polishing wear rates, measured to a depth resolution of about 20 nm, showed that each of the implanted disks wore 20% to 40% faster than nonimplanted layers. Auger analysis showed (1) Gaussian-like profiles of the N-implanted layer, but with somewhat enhanced oxidation of the surface, and (2) a sputter-limited implantation profile in the Ni-implantcd layer, with some vacuum carburization. Transmission electron microscope analysis indicated that polishing produced an α′-martensite layer in the mainly austenitic 304 surface, but that implantation of N transformed the martensite to austenite at the outermost layers and produced iron nitrides below. In addition. Nimplantation stabilized the austenite against martensite transformation during subsequent wear. Martensite vanished after Ni implantation because of sputter removal, not phase transformation, during Ni bombardment. The Ne-implanted layer remained predominantly martensite. Changes in wear rates and microstructures were confined to depths commensurate with the range of ions in the implanted layer. Several hypotheses on the effects of ion implantation on microstructureand wear are discussed.