An amperometric enzyme electrode tor the analysis of glucose Is described. The electrode uses a substituted ferrlcinlum Ion as a mediator of electron transfer between Immobilized glucose oxidase and a graphite electrode. A linear current response, proportional to the glucose concentration over a range commonly found In diabetic blood samples (1-30 mM), is observed. Data are presented on the Influence of oxygen, pH, and temperature upon the electrode. Results with clinical plasma and whole blood samples show good agreement with a standard method of analysis.