The discovery of insulin by Banting and Best In 1921 is the subject of many papers and one authoritative book (Bliss M. The Discovery of Insulin. Chicago: University of Chicago Press, 1982. See also Bliss M. Rewriting medical history: Charles Best and the Banting and Best myth. I Med Hist 1993; 48: 253-274.). This paper charts the introduction of insulin in England and examines its effect on medical practice. Before 1922 there were few effective drugs and only one (thyroid extract) which had to be taken continuously. Insulin was radically different; it restored weight and vigour and allowed survival in diabetic coma and after surgery but was potentially dangerous because of the possibility of hypoglycaemia, had to be given by injection, and the dose varied with the amount of food and exercise. The immediate questions to be answered after the supply of insulin was assured were how could such a powerful drug be kept out of the hands of ignorant people (a phrase used by The Times), who would administer it, and who would supervise the treatment? Within a year further problems were identified. Should the aims of treatment be the same as those in the starvation era? Could the diet be liberalized? How much biochemical monitoring was necessary? I set the scene by describing how, from Minkowski's announcement (1889) that pancreatectomy caused severe diabetes, most clinicians and physiologists believed that the pancreas (and specifically the islets of Langerhans) produced an internal secretion which controlled carbohydrate metabolism. After Murray's (1891) demonstration that myxoedema could be cured by thyroid extract, it was assumed that diabetes would soon yield in the same way. Yet by the beginning of the first World War most experts were pessimistic about isolating the hypothetical internal secretion and had pinned their hopes on starvation treatment. In the decade before the introduction of insulin the management of diabetes was grim; patients were kept in hospital for weeks or months, while their calorie intake and glucose excretion was meticulously recorded. They were in the wards of physicians with a strong interest in biochemistry whose forte was analysing urine not looking after patients. When the Medical Research Council set up a multicentre trial of insulin in late 1922 they enrolled the physician biochemists who produced the early publications and became the experts. The narrow views and innate conservatism of these doctors with the inflexibility of the system in (London) teaching hospitals meant that insulin treatment became a straightjacket for many patients. One of the few who adapted the treatment to the patient rather than vice versa was Dr Robin Lawrence, who himself started insulin treatment in 1923 and learned with his patients. At first the cost of insulin was high and there was concern that it would be used wastefully and that, if patients were given free rein, they would succumb to gluttony, It was hoped that diabetes was a simple functional weakness of the islands of Langerhans; if so, it was argued, pancreatic rest with insulin might lead to full recovery. The first, very malnourished, patients were treated with small doses to produce an average weight gain of 1lb in 15 days. There was a fear that with time insulin would lose its effectiveness but this soon proved groundless. Whether frequent blood sugar measurements were necessary was much debated but it was soon obvious that they were impractical. Hypoglycaemia was seen as a major danger by some physicians and it was worry about such a dangerous side effect and their inability to measure blood sugar which probably dissuaded general practitioners from initiating or supervising the new treatment. Insulin became generally available in June 1923 and within 3 years most of the principles which guide treatment today had been formulated, together with areas of controversy such as: Should normal blood sugars be the aim of treatment? Was alkali beneficial or dangerous in the treatment of coma?