NAD(P)H can be detected sensitively with peroxidase (POD)-entrapped and ferrocene (Fc)-embedded carbon paste electrodes in the presence of 1-methoxy-phenazine methosulfate (MPMS+), where MPMS+ catalyzes NAD(P)H oxidation with dioxygen to generate H2O2. It is essential to cover the PODiFc-CP electrodes using a suitable membrane with fine mesh in order for the sequential reactions to proceed stoichiometrically. Under suitable conditions, the current response showed a linear relation to the NAD(P)H concentration ranging from 0.1 to 40 mu M with a relative standard deviation of 3.4% (n = 6 at 1 mu M). The detection limit of NAD(P)H was 40 nM. This method was successfully applied to isocitrate dehydrogenase activity measurements in serum.