Abstract The design and testing of an amperometric glucose biosensor in which electrical communication between the flavin redox centers of glucose oxidase and a conventional carbon paste electrode has been achieved by using an electron-transfer mediator based on tetrabutylammonium–tetracyanoquinodimethane are described. The biosensor has been characterized by cyclic voltammetry and constant potential measurements. The biosensor responds rapidly to glucose; the time required to reach 95% of the steady-state current is less than 20 s. The response to glucose under N 2saturation shows an apparant Michealis–Menten constant K app Mof 47.0 mmol/liter. The biosensor can be operated in a potential range where the oxidation of common interfering species, such as ascorbic acid and uric acid, does not occur. The lifetime of the biosensor is 29 days and plasma glucose assays were correlated with spectrophotometry ( n= 8, r= 0.990).