The purpose of this review is to summarize the information and experience at present available on the intranasal administration of insulin to human subjects and to describe some of the anatomical, physiological, pharmaceutical and technological factors which can affect the absorption of insulin. An overview is given of those absorption promoters which have been used in clinical insulin studies, and the possible absorption-promoting mechanisms are discussed. This review shows that the nasal route offers a promising alternative to parenteral administration. The easier administration and the acceptance by the patients is encouraging the development of new intranasal insulin preparations.