Near-normal glucose tolerance tests in diabetic dogs were obtained during basal rate insulin infusions in restrained animals by use of extracorporeal infusion pumps and in conscious, unrestrained animals by means of implanted infusion pumps. Even better regulation of blood glucose in diabetic animals was obtained by the addition of predetermined pulses of insulin at higher flow rates than the basal flow rate, accomplished by use of a transcutaneously activated valve mechanism attached to the implanted infusion pump. We conclude that near-normal blood glucose concentrations can be maintained throughout the day in the dog by these means and that similar approaches, using implantable infusion pumps, in man may lead to better long-term control of diabetes than is currently available.