Aerosol drug delivery is widely used by patients with asthma and chronic bronchial obstruction for beta-2 agonists and anticholinergic drugs. More recently, inhaled steroid sprays have also been introduced. The efficacy of easy to use aerosol sprays is well proven and has become an important administration route. Different models of metered dose inhalers with gas propellants or dry powder devices help improve patients compliance. Nebulizers can be used in particular situations. Aerosol administration is proposed for anti-infectious agents and for rhDNase in cystic fibrosis. Aerosol delivery of nucleotides and antiproteases are currently under evaluation. Gene therapy can also benefit from the aerosol route which may be proposed in the near future for many different types of systemic treatments. Possible drugs include cyclosporin for lung grafts, prostacyclin for primary pulmonary hypertension, insulin for diabetes or morphine in certain types of dyspnea.