Faradaic impedance spectroscopy and chronopotentiometry are used as electrochemical methods for probing in situ bioaffinity interactions on surfaces between enzymes and their molecular or macromolecular cofactors. Alcohol dehydrogenase (E.C. 1.1.1.1.) and lactate dehydrogenase (E.C. 1.1.1.27) bind to an NAD(+)-functionalized monolayer electrode with association constants corresponding to 1.6 x 10(4) and 1.5 x 10(5) M-1, respectively. Cytochrome oxidase binds to an oriented cytochrome c monolayer assembled on an An electrode with an association constant of K-a= 1.2 x 10(7) M-1.