Aerosol therapy must be applied according to specific indications. Therapy ranges, anatomically, from smallest to largest airways; physically, from fine "dry" cool to dense heated mists; pharmacologically, from potent to bland agents. Bronchodilators in minuscule amounts are used to counter mucosal edema and bronchospasm and should be used with other agents. Bland mists are used to mobilize secretions. Mucolytics are used when less potent agents fail. Chest percussion and postural bronchial drainage are adjuncts to evacuate mobilized secretions. Antibiotic aerosols can treat bronchial infections failing to respond to systemic antibiotics. Antiinflammatory steroids have only limited applicability. Antifoaming agents are used in fulminant pulmonary edema when there is no response to oxygen and positive pressure ventilation. Cromolyn sodium blocks spasmogen release from type I reagenic antigen-antibody reactions and should be used prophylactically for allergic asthma.