Nine insulin-dependent diabetic patients were treated with continuous subcutaneous (s.c.) insulin infusion, using a portable battery-driven infusion pump and home monitoring of capillary blood glucose. The infusions were maintained for 4 days during an acute in-hospital study and for up to 150 days on ambulatory patients. No significant changes in growth hormone and cortisol secretory patterns were found at the end of the acute study. Mean plasma glucose, M values, and glycosylated hemoglobin A1 (HbA1), as well as the patients' sense of well-being, improved significantly. However, absolute normalization of metabolic control was not achieved, since patients presented occasional, albeit minor, swings of blood glucose. The possibility that the same improvement in control could be achieved with multiple s.c. injections of insulin and similar monitoring of blood glucose in the home is discussed. It remains to be seen whether the degree of control obtained will influence the development of the late complications of diabetes mellitUS.