The activity of glucose oxidase (GOD) is usually visualized with tetrazolium salts and intermediate electron carriers. Alternatively, staining of GOD can be performed by a coupled enzyme system. The cytochemical procedure involves a two-step enzyme method in which GOD (the enzyme as label) and HRP (the indicator enzyme) are coimmobilized onto the same cellular sites by immunological bridging or by other ligand binding principles such as avidin-biotin interaction (KUHLMANN WD and PESCHKE P 1986). In this coupled enzyme technique, H2O2 is generated by enzymatic reaction of GOD with D-glucose and, subsequently, generated H2O2 is serving as substrate for HRP in the oxidation of DAB (diaminobenzidine) or AEC (aminoethylcarbazole).