The electrochemical control of the redox reactions of vitamin B12 and derivatives thereof plays an important role for the in vivo investigations of the B12 dependent biological transformations. While most of these studies were performed in solution, electrodes coated with appropriate B12 derivatives are of more recent interest. A survey of our results in preparing electrodes bearing B12 derivatives is given. Structural features of the surface coating are discussed. Some of the electrodes show catalytic activity for the reduction of oxygen.