Abstract: A Method Validation Unit (MVU) for the evaluation of the level of sterilisation in a sterilisation method involving the use of a fluid at or near the supercritical pressure and temperature for that fluid, wherein the MVU comprises a sterilisation indicator housed within a gas-permeable container, wherein the sterilisation indicator comprises an indicator medium and a population of one or more colony forming units (CFUs), and wherein the indicator medium comprises one or more structural features representative of the internal structure of a material to be sterilised in the sterilisation method.