OF the materials which have been used for surgical prosthetics, the stellite alloys (based roughly on 65 cobalt, 30 chromium, 5 molybdenum) have excellent strength and adequate corrosion resistance1. Unfortunately these alloys are available only in the form of castings which, in the absence of any special techniques, develop a very large grain-size in the material. Small surgical implants have cross-sectional areas comparable to this grain size which may result in their mechanical properties being dependent on the random crystal orientation of a single grain to an applied stress. The strength of the implant may also be limited by weakness of the grain boundaries in the material. Any small amounts of impurity will segregate to the grain boundaries of the casting; when the grain size is large, the grain boundary area becomes relatively small and so the impurities may reach a high concentration. It is thought that both the foregoing factors are responsible for the wide variation and unpredictability of mechanical tests carried out here2-4. Therefore, a refined grain structure of these alloys should have beneficial effects by (a) giving a truly polycrystalline material, preferably of higher purity, and (b) spreading any impurities more uniformly throughout the material by increasing the grain boundary area.