An in vitro release testing (IVRT) device for orally inhaled drug products, for use in an IVRT apparatus, the device having an air-permeable filter loaded with particulate material representing a dose of an orally inhaled drug product. The device has an upper filter support element and a lower filter support element, the loaded filter being circumferentially retained between the upper and lower support elements, a filter cover to cover the upper surface of the loaded filter, and a filter cover retainer provided to assemble and seal the IVRT device.