Ring and split-disk plastic film carbon electrodes (PFCEs) were fabricated for use in thin-layer radial flow cells which were coupled to a microdialysis sampling system. PFCEs, were initially coated with osmium poly(vinylpyridine) redox polymer horseradish peroxidase (Os-gel-HRP). Then a second coat of oxidase enzyme was applied to produce enzyme bilayer (oxidase/Os-gel-HRP) PFCEs which were subsequently over-coated with cellulose acetate for use in the determination of glucose or lactate at 0 mV (vs Ag/AgCl). Split-disk electrode geometry enabled different oxidase enzymes to be immobilized on each half of a split-disk, Os-gel-HRP-coated, PFCE to facilitate the electrochemically independent yet continuous on-line determination of these two analytes from a single dialysate. In continuous-flow experiments, cellulose acetate overcoated oxidase/Os-gel-HRP cast-coated PFCEs were quick to stabilize background current and displayed linear and sensitive responses to substrates. The effect of ascorbic acid was minimal and cross talk between partner split-disk electrodes was demonstrated to be acceptable for in vivo applications. The utility of this analytical system is demonstrated by the quantitative on-line continuous assay of changes in dialysate striatal extracellular glucose and lactate from a conscious rat during (a) local stimulation of neurons by perfusion with the depolarizing agent, Veratridine, and (b) physical restraint.