The present invention provides the use of IFN-.beta., an agent that increases the expression of IFN-.beta., or a polynucleotide which is capable of expressing IFN-.beta. or said agent for the manufacture of a medicament for the treatment of rhinovirus-induced exacerbation of a respiratory disease selected from asthma and chronic obstructive pulmonary disease, wherein said treatment is by airway delivery of said medicament, e.g. by use of an aerosol nebuliser. Also provided is IFN-.lamda. for the same purpose.