Abstract: An apparatus (100) that simulates breathing, which is suitable for use when testing inhalers (14), comprises an inlet (22) to which, in use, an inhaler (14) can be connected, and a vacuum pumping system, which has a vacuum pump (106), a high-speed valve (102) and a flow sensing means (137, 112, 104, 114) interposed between the inlet (22) and the vacuum pump (106), and a controller (126). A user interface (134) enables a user to input a target flow profile (148, 150), which may correspond to human inspiration, such that, in operation, the controller (126) can control the operation of the vacuum pump (106) and the high-speed valve (102) so that the pressure and/or flow rate within the apparatus (100) matches the pressure (150) and/or flow rate (148) of the target flow profile in real-time or near-time.