The corrosion susceptibility of Ti, Ti}6Al}4V and Ti}45Ni was studied in a bu!ered saline solution using anodic polarisation and electrochemical impedance measurements. Pitting potentials as low as#250 mV(SCE) were recorded for Ti}45Ni and once initiated pits continued to propagate at potentials as low as !150 mV(SCE). It was possible to increase the pitting potential of Ti}45Ni to values greater than #800 mV(SCE) using a H O surface treatment procedure; however, this surface modi"cation process had no bene"cial e!ect on the rate of pit repassivation. Impedance spectra, recorded under open-circuit conditions, were modelled using a dual oxide "lm model; a porous outer layer and an inner barrier oxide layer. The nature of this porous outer layer was found to depend on the nature of the electrode material and the presence of phosphate anions in the saline-bu!ered solution. The porous layers formed on Ti}45Ni and Ti}6Al}4V in the presence of phosphate anions had low resistances typically between 10 and 70 cm . Much higher porous layer resistances were recorded for Ti and also for Ti}45Ni and Ti}6Al}4V in the absence of the phosphate anions.