A metered dose inhaler (1) has a pressed aluminium vessel, to which is crimped at a neck (2) a valve housing (3) having a dispensing spout (4). Within the vessel is a piston (5), urged by a spring 6 into contact with the medicament liquid (7). A bearing ball (8) is included in the medicament liquid. As the medicament liquid is dispensed in successive doses, the piston is kept in contact with the liquid (7) by the spring (6), with an edge seal (9) ensuring that the liquid does not pass to the spring side of the piston. As the medicament liquid is dispensed, the piston begins to restrict the movement of the ball, until it is scarcely able to move longitudinally of the vessel. This change is discernible as a change in noise of the rattle. Thus the user can know whether there is plenty of medicament liquid left and when he needs to use a new inhaler.
