Bilirubin oxidase (EC 1.3.3.5) catalyzes the oxidation of bilirubin to biliverdin with the concurrent reduction of oxygen to hydrogen peroxide. A platinum electrode was prepared with an immobilized bilirubin oxidase membrane. Bilirubin was determined by monitoring the increase in hydrogen peroxide concentration from the enzyme reaction. The calibration plot for bilirubin shows linearity up to 300 pM. The detection limit is 0.7 pM.