The inhalation route is widely used for the treatment of obstructive lung diseases, because administered drugs have a high therapeutic index as they reach their target directly; this requires that they be of adequate size to penetrate the conducting airways, i.e. 2-5 microns. Pressurized inhalers were the first reliable metered-dose devices available, and are still the most frequently used. However, metered-dose inhaler (MDI) suspensions will have to be reformulated: they contain chlorofluorocarbons (CFCs), whose production has to be stopped within a few years, as they affect the stratosphere. Another limitation of MDI usage is paradoxical bronchospasm; this phenomenon, however, occurs in a low number of patients and is rarely clinically relevant. The main cause of concern with MDIs is their misuse by more than 50% of patients, which leads to a reduced lung deposition and clinical efficacy. Therefore, other inhalation devices have been developed: spacers, dry-powder inhalers (DPIs), and breath-actuated MDIs have been shown to increase lung deposition of drugs in poor coordinators. However, all have limitations which may have varying consequences on clinical efficacy: cumbersome dimensions of spacers, effect of inspiratory flow rate and humidity on lung deposition of dry powders, need for reformulation with CFC-free gases for breath-actuated pressurized inhalers. Reformulation of MDI aerosols is a complex procedure, which may not be feasible for all drugs. The new products need extensive toxicological and clinical testing, as some of their characteristics may differ from those of their predecessors.