Insulin administered nasally has considerable potential for the treatment of both insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetes. For patients with NIDDM it is possible to prevent preprandial hyperglycaemia and postprandial hypoglycaemia by employing a suitable and properly timed intranasal insulin dose. The low bioavailability of simple formulations of insulin can be greatly improved by using absorption enhancers or novel delivery systems such as bioadhesive microspheres. The need for nontoxic and nonirritant systems is stressed.