Coimmobilization of L-lactate oxidase (LOD) and L-lactate dehydrogenase (LDH) on a film bound to an oxygen electrode makes it possible, by recycling L-lactate and pyruvate, to lower their detection limit to 10 nM. With LOD immobilized alone and LDH in solution easy LDH measurements were performed. The detection limit was 1 IU l(-1). Similarly, this mixed biosensor, using an LDH sensitive to mercurials, was used for p-chloromercuribenzoate (PCMB) detection. Coimmobilization of LOD + LDH with an NAD(+)-dependent dehydrogenase allows the measurements of all dehydrogenases. NAD(+) is recycled. The detection limit was 50 nM. Applications can be found in medicine, the food industry, and the environment.