Abstract: There is disclosed apparatus for producing an aerosol having an atomising chamber having an inlet for material to be atomised, means for atomising the said material, outlet means for the aerosol produced and, inlet means for air, air supply means comprising an air inlet, blower means and an air outlet, means connecting the air outlet of the air supply means to the air inlet of the atomising means and a filter for removing bacteria from the air supplied by the air supply means and drive means connected by a magnetic coupling to the blower means.The blower means is preferably a fan wheel which is arranged to suck air through the filter, the fan wheel being arranged in a separate chamber which is in the form of a replaceable cassette which can be inserted into the housing of the apparatus, the magnetic coupling acting through a closed wall of the cassette.