This paper describes the instrumentation of a full-scale test, known as the Multi-Purpose Test, of the KBS-3H spent nuclear fuel design alternative carried out in the Äspö Hard Rock Laboratory (Sweden). This test is part of the Large Underground Concept Experiments EU project, where Posiva and Svensk Kärnbränslehantering are partners. The test consists of two aspects. The first is that of a ‘demo’ test whose aim is to check the manufacturing and installation process of the different components of the KBS-3H design. The second is the instrumentation and monitoring of the test system. The test is carried out under isothermal conditions and the scope was to measure component displacements, the hydration and swelling pressure of the bentonite material and the water pressure in host rock.