The electropolymerization of a flavin reductase (Fre) - amphiphilic pyrrole ammonium mixture previously adsorbed on the electrode surface provides an efficient bioelectrode for the amperometric detection of NADH and NADPH. The bioelectrode response was based on the oxidation at -0.1 V vs. SCE of the enzymically generated dihydroriboflavin. The sensitivity and detection limit of the bioelectrode were 29 mAM-' cm-' and 0.2pM for NADH and €5.8mAM-' cm-' and 0.4pM for NADPH. The coimmobilization of Fre and a lactate dehydrogenase leads to a dehydrogenase-based biozlectrode for the determination of lactate in the presence of riboflavin and NAD'. With laponite additives into the polypyrrole host matrix, the sensitivity and the detection limit of the bioelectrode for lactate are 11.7 m.4M-I cm? and 1 pM respectively. Owing to the negative value of the applied potential for the oxidation of riboflavin, the response of the bienzyme electrode remains insensitive to interferents like ascorbate, urate and acetaminophen.