According to one aspect of the present invention, an accessory for an aerosol inhalation system includes a main conduit body having an outlet end for placement close to a mouth of a patient, and first and second leg conduits that are in fluid communication with the main conduit body. The accessory further includes a holding chamber having a first compartment and a second compartment separated from the first compartment, with the first compartment being sealingly and fluidly coupled to the one port associated with the first leg conduit and the second compartment is sealingly and fluidly coupled to a port associated with the second leg conduit. An arrangement of valves is provided for directing fluid along prescribed flow paths depending on whether the patient inhales or exhales.