Recent controlled clinical trials have confirmed the usefulness of aerosolized tobramycin in cystic fibrosis and have emphasized the importance of ensuring adequate lung delivery of inhaled antimicrobials. For purulent tracheobronchitis associated with prolonged mechanical ventilation it has recently been established that it is possible to deliver substantial and measurable doses of medications to the airway via aerosolization, but controlled studies are needed to determine the efficacy and safety of inhaled antibiotic therapy in this setting. However, prophylactic aerosolized antibiotic therapy in an intensive care unit setting may be counterproductive. Aerosolized pentamidine continues to provide prophylaxis against PCP in a substantial minority of subjects with human immunodeficiency virus infection who are intolerant of oral agents. The effectiveness of aerosolized amphotericin B as prophylaxis against aspergillosis in neutropenic patients needs to be evaluated in a large clinical trial. Zanamivir, an inhibitor of neuraminidase, delivered via inhalation, shows promise in the treatment of uncomplicated influenza infection, but more data are needed on its effectiveness and safety in patients with preexisting respiratory disease. The development of new chemical entities, more efficient delivery systems, and more precise measurement of dose-response and regional pulmonary drug distribution of inhaled antimicrobials suggest that this somewhat neglected topic in therapeutics may be about to receive an increased degree of attention.