We have investigated the effects of boron ion implantation on the wear behaviour of 304 stainless steel. The initial phase composition of the specimens was varied by using two different kinds of polishing technique. Electropolishing resulted in purely f.c.c. (austenitic) specimens. Subsequent mechanical polishing resulted in a phase transformation that introduced a b.c.c. (martensite) phase. The specimens studied were either electropolished or fully polished (electropolished and mechanically polished). In general, we observed that boron implantation improves the wear performance of the steel. The result of boron implantation is to inhibit hardening of the surface during wear, as was seen from measurements of the microhardness inside the wear tracks. (Such hardening has previously been shown to occur in studies on unimplanted material, through martensitic transformation, and leads to the formation of a brittle surface sheet that is prone to cracking.) Interestingly, the improvement on implantation and the associated inhibition of hardening in the wear tracks were seen to be much more pronounced when full polishing was employed rather than just electropolishing, i.e. when the specimen contained a small amount of martensite prior to implantation. The measurement of the microhardness inside the wear tracks provided a quick method of assessing the transformation during the wear process, which we then correlated with the friction and wear behaviour in each case. Measurements of the microhardness on as-implanted surfaces showed that a fully polished surface strengthens to a greater extent than an electropolished surface. This appears to result in reduced plastic deformation, leading to the observed reduction in transformation during wear and, thus, could explain the greatly improved behaviour.