The dual-ion implantation of titanium and carbon (4.6 × 10 17 Ti ions cm -2 at 180 keV followed by 2.0 × 10 17 C ions cm -2 at 50 keV) into 304 stainless steel was found to reduce friction and wear in vacuum, oxygen and air environments. Unlubricated friction measurements and wear track analyses were carried out in situ in a scanning Auger microprobe using a 440C pin at a hertzian contact stress 3 times the bulk yield strength of unimplanted 304 steel. In ultrahigh vacuum the friction coefficient was reduced from 1.2 to 0.6 – 0.8, while the wear track width decreased from 414 to 325 μm at 5000 cycles. In oxygen at a partial pressure of 2.1 × 10 -5 Pa almost the same reductions in friction and wear were obtained as in air: ion implantation decreased the friction coefficient from 1.10 to 0.65 and the wear track width from 319 to 198 μm at 5000 cycles, compared with decreases of 1.0 to 0.5 and 255 to 190 μm respectively in air. Such decreases were not observed in nitrogen ambients, for which the results were similar to those in ultrahigh vacuum. Friction coefficients and the analyses of wear track compositions indicate that oxidation of the implanted layer during sliding reduces friction.