Corticosteroids are the most potent anti-inflammatory agents used to treat chronic inflammatory diseases such as bronchial asthma. However, there are a small number (50% of the health care costs of asthma. If the mechanisms for corticosteroid insensitivity are understood they may, in turn, provide insight into the key mechanism of corticosteroid action and allow a rational way to treat these individuals whose disease tends to be severe. Corticosteroid insensitivity is not limited to asthma and is a feature of other inflammatory diseases, such as rheumatoid arthritis and inflammatory bowel disease. Thus, elucidation of the cause for the relative lack of corticosteroid response in this subgroup of asthmatic individuals may have important implications for other diseases.