Effective treatment of diabetes mellitus became possible when Banting and Best isolated and purified insulin in 1921. Commercial extraction and purification followed, leading quickly to widespread clinical use. At first it was hoped that insulin would "cure" diabetes. Unfortunately, as patients began to survive for years, a host of disabling or lethal vascular, renal, ocular, and neurologic problems developed in many. It was natural to assume that these complications were caused by prolonged hyperglycemia, and a belief arose that normalization of blood glucose concentrations would prevent or delay their occurrence. This assumption has been difficult to prove, although it is supported by evidence accumulated during the past decade.
Unfortunately, the conventional methods of treating insulin-dependent diabetes during the past three decades have seldom been adequate to normalize or nearly normalize blood glucose concentrations. During the past three years, however, new techniques have given hope for improved control. The purpose of