INS and diabetes mellitus: A second reason why treating diabetes with oral inhalation of insulin is the best example of the expanding role of aerosol therapy into systemic drug delivery is because what we now know about systemic drug delivery of peptides by inhalation was learned during the development of inhaled insulin and the study of its success and early failure continues to inform future development of systemic drug delivery by inhalation, as well as other new applications of aerosol therapy.