A theoretical study of polymeric catalytic membrane reactors (PCMR) is performed when a reversible A <-> B reaction is taking place inside the catalytic membrane. The PCMR is assumed to be isothermal, and with a perfectly mixed flow pattern for both retentate and permeate chambers. An analytical expression is derived to calculate the reactor conversion and the reactor conversion enhancement for the case in which the membrane permeability is the same for the reactant and product. When the membrane has different permeabilities for the reactant and product, a semianalytical solution is presented. The results show that, at least theoretically, conversion above thermodynamic equilibrium can be achieved with the PCMR when the membrane has higher permeability for the product than for the reactant. It is also pointed out that, in the PCMR, the environment of the catalyst particle should be quite different from that existing in conventional reactors. This should change the properties of the catalyst particle and it must be carefully considered. (c) 2006 Elsevier B.V. All rights reserved.