the electrochemical and spectroscopic behavior of the phenoxazine-type mediator nile blue a adsorbed on glassy carbon (gc) and ag electrodes has been examined. the ph dependence of the formal redox potential and the ph dependence of the catalytic oxidation of nadh were found to be similar, although not exactly the same, on both types of electrodes. those differences that were observed may be attributed at least partially to multilayer formation on gc, whereas only one monolayer is present on ag (e.g., the catalytic current for nadh oxidation was much greater for gc than for ag). for both electrodes, the catalytic peak was shifted several hundred millivolts more positive than the e $degree$ $prime$ value of adsorbed nile blue a. this shift is attributed to the formation of a nile blue a/nadh complex. the rr and serrs spectra of the mediator on both gc and ag electrodes were very similar. changes in the spectra as a function of ph are interpreted to reflect changes in nile blue a orientation at both electrode surfaces. two distinct species were detected in the serrs spectrum of nile blue a in the presence of nadh. these are assigned to nile blue a and a complex between nile blue a and nadh. (author abstract) 29 refs