CONCLUSIONS Drug delivery to the lung by aerosol inhalation can only be accomplished in high doses (tens of milligrams) by repetitive inhalation. In such cases, administration from a restricted menu of ultrasonic or jet nebulizers is most appropriate. Doses less than or equal to about 4 mg can potentially be delivered from avarietyofsingle-dose–meteringinhalers.TheMDIandpassive DPI are presently the least expensive to develop. However, unless significant modifications are added to these technologies, they rarely offer high delivery efficiencies to lung. New aerosol drug development efforts need to seek to identify the clinical importance of efficient “targeted” drug delivery to different re- gions of the respiratory tract.Novel technologies should be cho- sen in cases in which significant clinical advantage is expected to result from efforts to increase delivery efficiency and/or the targeting of specific regions. New electromechanical inhalers offer high delivery efficiencies, a choice of particle size distribu- tions, and improved methods of ensuring patient compliance. Whether these are worth the high cost of development will depend on the added value that they bring to drug therapy in each specific case.