Two patients with asthma developed an anaphylactic reaction after the intravenous administration of hydrocortisone. In both cases, the reaction included the rapid development of airflow obstruction. Previous reports have suggested that the allergenic component may be hydrocortisone itself, rather than the diluents or preservatives. When administering hydrocortisone, one should be aware of the possibility of such a reaction, even though it is uncommon. Although potentially life-threatening, particularly in an asthma sufferer, this reaction should be reversible with prompt recognition and appropriate management.