The recent development of inhaled insulin for the treatment of diabetes has the potential to significantly improve patient compliance and diabetes control. Preliminary studies have shown inhaled insulin to be effective in lowering blood glucose and HbA(1c) levels. However, inhaled insulin may stimulate insulin antibody production more than is commonly observed with highly purified human insulin administered subcutaneously. The significance of insulin antibodies in patient care has been a topic of frequent debate and has been studied extensively. This review will discuss the potential implications of elevated insulin antibody levels, the role insulin antibodies play in the metabolic control of diabetes and the effect inhaled insulin may have on the immune system.