Medical grade alumina in a porous form, as well as the normal dense form, have been tested in a crossed-cylinder wear machine under conditions which reproduce those to be found in heart valves. The results show steady wear rates. For dense alumina pairs this rate is 9.9 × 10–7 mm3 (Nm)–1; for porous pairs it is about 10 times higher. A dense alumina valve prosthesis using a hinge mechanism is estimated from this data to have a useful life of about 45 years.