A dry powder inhaler has a main airflow path including a cyclone chamber (16) having an air inlet and being so shaped that at least a part of the chamber decreases in cross-sectional area in a direction away from the air inlet, so as thereby in use to set up a reverse flow cyclone in the chamber. A bypass airflow path (8) bypasses the cyclone chamber and the main and bypass airflow paths communicate with a mouthpiece (6). The cyclone chamber may be provided by a part (22) which is removable from the rest of the inhaler for regular replacement thereof.