The alloy Ti‐6Al‐4V has been implanted with carbon and nitrogen ions. The microstructure produced by these implants is found to contain fine particles of TiC and TiN, respectively. Rotating beam fatigue tests show improved fatigue life for both implants, with the superior carbon implantation giving a 20% increase in endurance limit and a factor of 4–5 lifetime increase at higher stresses over unimplanted material. A dose of 1×1017at./cm2is required to obtain the maximum effect. Fatigue cracks have been observed to originate up to 150 &mgr;m below the surface, indicating a complex interaction between the implanted layer and the fatigue failure process.