Miniaturized urea and glucose sensors prepared by immobilization of glucose oxidase or urease directly onto all solid-state contact PVC-NH2 membrane ammonium and hydrogen ion selective electrodes are described. The resulting biosensing membranes function equivalently to normal PVC membranes in terms of potentiometric response properties. The most important features of the glucose and urea sensors were high sensitivity, long life-time, easily built at a low cost, microconstruction and short response time. The characteristics of the glucose and urea sensors were examined in several buffer solutions at different concentrations and pH values. The influence of immobilization conditions on the dynamic response properties and life-time of the electrodes was studied. Under optimal conditions, the urea electrode showed a linear response between 5 x 10(-2) and 5 x 10(-4) M urea, while the glucose electrode showed a linear response between 5 x 10(-2) and 1 X 10(-4) M glucose. (C) 2002 Elsevier Science B.V. All rights reserved.