A pharmaceutical aerosol formulation to be administered by a pressurized metered dose inhaler which comprises as active ingredient (R,R)-(±)-formoterol fumarate in a concentration comprised between 0.003 and 0.192 % w/v, in a solution of liquefied HFA 134a propellant and anhydrous ethanol as co-solvent, wherein the pH is comprised between 3.5 and 4.0 and is adjusted by adding hydrochloric acid, characterised in that the amount of residual water is less than 1500 ppm on the total weight of the formulation and that the fraction of particles equal or less than 1.1 µm delivered on actuation of the inhaler is higher or equal than 30% as defined by the content of the stages S6-AF of an Andersen Cascade Impactor, relatively to the content of the stages S3-AF, according to the method referred to in European Pharmacopoeia, second edition, 1995, part v.5.9.1, pages 15-17.
