Abstract: Apparatus is described for controlling blood glucose concentration in a subject by selected infusion of insulin and/or glucose, depending upon the general blood glucose concentration. This apparatus comprises in combination sensor means for measuring the blood glucose concentration and for providing computer input signals based on such measurement, computer means for receiving such input signals and being programmed to provide output signals based upon such input signals, and pump means responsive to such computer output signals to supply insulin and/or glucose to such subject at a rate determined by such output signals. The computer derives the output signals in accordance with specific quadratic and biquadratic equations employing certain independently selected values relating to basal blood glucose concentrations and basal insulin and glucose infusion rates at such basal blood glucose concentrations.