Hydroxyapatite (HA), Ca-5(PO4)(3)OH, is a biologically important material that occurs naturally in bone. Synthetic HA is thus a natural choice as a surface coating for materials that are used in implant surgery due to its inherent biocompatibility. HA coatings can be applied by several techniques, one of which is vacuum plasma spraying (VPS). This method is used commercially to apply HA to a titanium alloy substrate. A complete characterization of the initial, as-sprayed surface state was carried out using scanning electron microscopy (SEM), x-ray diffraction (XRD), and also atomic force microscopy (AFM). XRD measurements reveal the coating to be semicrystalline and SEM observations showed it to be irregular in appearance but with flatter regions interspersed, Large scale AFM scans (> 20 mu m) of the as-sprayed coatings were difficult to obtain as the tip would frequently snag on higher outcrops, sometimes snapping the cantilever in the process. To prevent this from occurring, the scan range was reduced and images were only obtained within the flatter regions observed previously with SEM. From these data, the roughness values characterizing the flatter surfaces were estimated. Further, ex situ images of the coatings after they had been aged for periods of up to 28 days in a solution simulating the physiological environment within the body (buffered Ringer’s solution) were obtained. Changes in the topography were observed that may have a bearing on processes such as the cellular response of the surrounding tissue to the implanted material. The structural changes in the surface were again characterized by estimating the surface roughness values. Conclusions are drawn regarding the formation of the coating from plasma spraying and also the importance of the dissolution process in promoting bony ingrowth and rapid fixation of the implant.