The essential components of an intensive insulin therapy program are maintenance of stable basal concentrations of insulin between meals and appropriate, timely increases in the concentration of circulating insulin after ingestion of meals. Closed-loop systems that both continuously monitor the plasma glucose concentration and continuously infuse insulin intravenously can reproducibly achieve near-normal glycemia in patients with insulin-dependent diabetes mellitus. Near-normal glycemia can also be achieved with use of a continuous subcutaneous insulin infusion (CSII) or multiple daily injections (MDI) of regular insulin combined with a single injection of slowly absorbable insulin in properly selected, compliant and cooperative patients. The frequency of hypoglycemia is similar with CSII and MDI. The risks of catheter-associated problems and ketoacidosis, however, are greater with CSII than with MDI. In contrast, the basal concentration of insulin can be more reproducibly and rapidly regulated with CSII than with MDI. The ratio of risk versus benefit associated with intensive insulin therapy with either CSII or MDI is currently unknown.