As a chronic inflammatory disease, much of the research related to asthma has been focused on proinflammatory mechanisms. Recently, advances have been made in defining mechanisms that control inflammation and induce immune tolerance to specific antigens. Subsets of CD4(+) cells known as T regulatory cells play an important role in directing these processes, and recent experiments have begun to define crucial molecular and signaling pathways. There is a growing body of evidence describing the function of T regulatory cells in the development, disease activity, and treatment responses related to asthma and other atopic diseases. Collectively, this new information suggests that a greater understanding of these pathways might lead to new therapeutic targets for asthma and other diseases of chronic airway inflammation.