Titanium ions were implanted into Ti-6A1-4V to investigate the effects of implantation-induced residual stresses on hardness. Fluences ranged from 0 to 4.0 × 1017 cm-2, at 0.5 × 1017 cm-2 increments. Hardness values were obtained on unimplanted specimens, under various levels of bending stress, for estimation of ion-induced residual stresses in implanted specimens. The results showed that hardness increased with increasing ion fluence, up to 3.5 × 1017 cm-2, to a value that correlated with a bending stress of around 400 MPa. At the 4.0 × 1017 cm-2 fluence, the hardness dropped significantly. AFM images showed 'nodules' at this fluence, suggestive of buckling of the over-compressed surface layer. Surface texturing due to Ti implantation was evident at all fluences, suggestive of sputtering through the native oxide layer. © 1997 Elsevier Science S.A.