Microvascular complications of diabetes can be forestalled by effective glycemic control. However, the inherent limitations of standard subcutaneous insulins reduce their ability to control glycemia without risk of significant hypoglycemia and hyperinsulinemia. Hypoglycemia is unacceptable for most patients and may be dangerous. Hyperinsulinemia is undesirable because it causes weight gain and it has a putative association with atherosclerosis. This paper summarizes the major historical improvements in insulin therapy, and calls attention to the fact that none of the presently available commercial preparations in any combination is capable of simulating the profile of normal insulin secretion--the latter being regarded as the most effective means of normalizing glycemia. For this reason, a variety of new approaches to simulating the pharmacokinetics or glucodynamics of insulin secretion are under investigation. Fast-acting insulin analogues suitable for subcutaneous injection have been developed and appear to mimic the physiological insulin response more closely than standard insulins. Less progress has been made with basal insulins. Intravenous insulin has pharmacodynamic advantages but practical disadvantages of administration. Nasal insulin would be an attractive treatment modality only if its bioavailability could be significantly increased and its safety assured. Other interventions which improve glucose metabolism without necessarily simulating normal insulin secretion are under investigation. These include biosynthetic human C-peptide, insulin-like growth factor-1 and glucagon-like peptide 1 (7-36 amide).