The present invention provides a medicinal aerosol suspension formulation for MDI administration, comprising: a) micronised ² 2 -agonist; b) micronised corticosteroid; c) a sub-therapeutic quantity of a moisture-scavenger excipient; and d) a HFA propellant; wherein (a), (b) and (c) and their respective relative amounts are selected such that they associate to form floccules having a density substantially the same as that of the HFA propellant.