The steady-state solution of continuous conjugated enzyme reactions was theoretically obtained by application of the Theorell-Chance reaction mechanism for the system of alcohol dehydrogenase and lactate dehydrogenase immobilized in an ultrafiltration hollow-fiber tube. The reactor was a dialyzer of complete mixing type. The coenzyme, NAD, was dynamically recycled between its oxidized and reduced state by the action of the conjugated enzymes under continuous operation. The results of numerical calculation elucidated the dependence of NAD recycle number on such conditions as concentration of immobilized enzyme, feed concentrations of NAD and substrates, permeability, reactor volume, flow rate and fractional volume of fiber packed in a reactor. With a sufficiently high enzyme concentration and a low NAD concentration, a very high NAD recycle number (>1000) with a good conversion of substrate (>50%) was theoretically possible through the strong affinity between the enzymes and the cofactor. The cost of cofactor in an immobilized enzyme reaction may be greatly reduced by the present method of dynamic recycling.