Although subcutaneous insulin infusion from portable pumps is the current optimal therapy for type 1 diabetic patients, implantable pumps using the intraperitoneal route allow increased blood glucose stability and lowered incidence of severe hypoglycemia. Subcutaneously implanted enzymatic glucose sensors provide continuous interstitial glucose monitoring, but this may differ from the real-time blood glucose levels. Preliminary investigations of intravascular enzymatic sensors demonstrate their clinical acceptability and accuracy and the possibility of developing closed-loop insulin delivery by combination with implantable pumps.