Samples of a cobalt-based alloy that underwent a surface treatment were evaluated. The samples, which were obtained by casting alloy ASTM F 75, were ground and polished on one side until a mirror finish was obtained. The samples were encapsulated in wollastonite(W) using uniaxial pressure, treated at 1 220 ℃ for 1 h and subsequently tempered in water. The characterisation of the sample indicated that part of the ceramic encapsulating material was mechanically incorporated on the metallic surface by growth of the oxide layer of the alloy. After thermal treatment, a series of specimens were submerged in a solution with 5-fold simulated body fluid(5SBF) for 3, 5 and 21 days. Characterisation by scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD) indicated nucleation and growth of a homogenous layer of apatite, beginning on the third day when the sample was submerged. Samples of a cobalt-based alloy that underwent a surface treatment were evaluated. The samples, which were obtained by casting alloy ASTM F 75, were ground and polished on one side until a mirror finish was obtained. The samples were encapsulated in wollastonite (W ) using characterization of the sample indicated that part of the ceramic encapsulating material was mechanically incorporated on the metallic surface by growth of the oxide layer of the alloy. After thermal treatment, a series of specimens were submerged in a solution with 5-fold simulated body fluid (5SBF) for 3, 5 and 21 days. Characterization by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) indicates nucleation and growth of a homogenous layer of apatite, beginning on the third day when the sample was submerged.