A BS T R AC TThe adverse influence that substrate sequestration exerts on the performance of a continuously operated, plug-jlow enzymic reactor was studied both experimentally and theoretically. Thus, glutathione-S-transferase was immobilized on activated agarose, and its performance in a packed-bed reactor, both in the presence and in the absence of bovine serum albumin as sequestrutor, was investigated. In parallel, an analytical model was developed, accounting for the behavior of systems which obey Michaelis-Menten kinetics, and which involve substrate sequestration and product inhibition. Substrate conversion in the reactor was found to decrease as sequestrator concentration andlor substrate-sequestrator association constant increased.