A system for delivery of aerosol therapy to spontaneously breathing patients comprises a housing which defines a chamber. The housing has a base, a top and a main body extending between the base and the top. An ambient air inlet is located adjacent to the base and is normally closed by an inlet valve. The housing also has a patient port for receiving a mouthpiece or a face mask. The mouthpiece has an exhaust outlet closed by an exhaust valve. Similarly, the face mask has an exhaust outlet closed by an exhaust valve. Exhaled air is exhausted through the valves and to prevent recirculation through the chamber which would adversely affect dose efficiencies. The housing also has an aerosol port for receiving a vibrating mesh aerosol generating device. The aerosol port is located in a side of the main body of the housing for delivery of aerosol into the chamber between the inlet valve and the patient port. A boss extends upwardly from the base and is spaced-apart inwardly of the main body of the housing to define a reception space or well.