A valved holding chamber (2) includes a main chamber housing (49 and a mouthpiece assembly (6) removeably coupled to a first end of the main chamber housing, the mouthpiece assembly including a mouthpiece housing (24) having a mouthpiece portion (32) and a valve housing portion (30), a retaining ring (28) provided within and coupled to the valve housing portion, and a one-way inhalation valve (26) having an annular valve seat member (52), wherein the valve seat member is held between the retaining ring and an engagement surface of the valve housing portion. In one particular embodiment, a portion of the first end of the main chamber housing engages the bottom of the valve seat member and creates a seal between the main chamber housing and the one-way inhalation valve and between the one-way inhalation valve and the mouthpiece housing.
