Glucose dehydrogenase (E.C. 1.1.99.17) has been used to produce an amperometric enzyme electrode for glucose. With phenazine ethosulphate as the electron mediator, a linear response for up to 0.8 mM glucose was obtained with response times of 3–5 min. 2,6-Dichlorophenolindophenol as mediator gave long (> 30 min) response times, but the measurement time was reduced to 30 s by monitoring the first-order differential of the response; the derivatised signal allowed temporal separation of the enzyme-mediated signal from electrochemical interference. Whole blood glucose measurements were correlated with a spectrophotometric method based on glucose oxidase (y= 0.84x + 0.67, r= 0.963, n= 36).