Drugs for the treatment and prophylaxis of asthma are delivered to the lungs by inhalation and this is facilitated by the use of pressurized metered dose inhalers (pMDIs), pMDIs with spacer devices and dry powder inhalers (DPIs). Lung deposition of drugs from pMDIs depends upon both the physicochemical nature of the aerosol formulation and the patient's inhalation technique, however, the majority of the dose from a pMDI is deposited in the oropharynx. Large volume spacer devices can reduce oropharyngeal deposition; however, lung deposition may be increased or decreased with a spacer in comparison with a pMDI, according to the design of the spacer, the aerosol formulation, the patient's inhalation technique and the extent to which the electrostatic charge on the spacer is controlled. Lung deposition of drug from DPIs also varies according to the design of the device. One DPI, Turbuhaler, deposits twice as much drug in the lungs as a pMDI, has a lower intersubject variability of lung deposition and results in lower oropharyngeal deposition.