Abstract: An inhaler for dispensing a plurality of doses of particulate material has means for receiving and retaining a container (20) having a plurality of compartments, each for holding a respective dose (or part thereof). The container is moved by an indexing mechanism so as to bring successive compartments into registry with an airway to enable the contents of each compartment to be dispensed through the airway (50). The indexing mechanism is operated by a control member (6) which is movable through a series of alternating advance and return strokes (preferably rotational movements), the inhaler including a non-return mechanism (112, 114, 116 and 104) for preventing movement of the member in the direction of each return stroke before the completion of the respective preceding advance stroke, thereby to help to ensure that the indexing mechanism is properly operated.