Bronchial asthma and allergic rhinitis are among the most common diseases of modern society and to an increasing degree a major cause of illness, hospitalization, loss of productivity, and death. Despite improvements in drug therapy over the years, the incidence is still increasing. Inhaled and intranasal corticosteroids are the drugs of choice in the therapy of asthma and allergic rhinitis. Inhalation and intranasal use result in better, target-specific delivery of corticosteroids. Higher concentrations at the site of action and minimized systemic exposure provide improved therapeutic ratios. However, there is still considerable concern over the risk of systemic side effects. It is the goal of inhaled and intranasal corticosteroid therapy to produce long-lasting therapeutic effects at the site of action and minimize systemic side effects with high clearance, low oral bioavailability and high plasma protein binding. This article reviews the pharmacokinetic and pharmacodynamic properties of corticosteroids used in asthma and allergic rhinitis.