The most recent literature in the field of membrane reactors is reviewed, four years after an analogous effort of ours (Saracco et al., 1994), describing shortly the potentials of these reactors, which now seem to be well established, and focusing mostly on problems towards practical exploitation. Since 1994, progress has been achieved in several areas (sol-gel deposition of defect free sol-gel derived membranes, reduction in thickness of Pd membranes, synthesis of zeolite membranes) whereas stagnation was noticed in some others (high-temperature sealing of membranes into modules, scaling-up of membrane reactor, etc.). As a result, despite the still increasing research efforts, industrial application does not seem to be round the corner, yet. However, several non-permselective membrane reactor opportunities with currently available membranes might pave the way for more sophisticated applications.