The goal of this work is to evaluate the potentialities of MWs for synthesising sodalite/alphaAl(2)O(3) membranes on tubular supports using hydrothermal conditions. The method allows the synthesis of promising surface films and infiltrated membranes. However, with the conditions used in this work, the dissolution of the a-alumina support revealed a disturbing phenomena for both the reproducibility and scaling-up of the direct membrane synthesis. In order to overcome this problem, another indirect strategy has been also considered: the pre-seeding/secondary growth method which allowed the synthesis of larger and homogeneous samples with a good reproducibility. The membrane quality was evaluated by single gas permeation studies with both N-2 and He. In the studied range of temperature 20-165 degreesC, gas transport was essentially governed by adsorption and surface diffusion, yielding a maximum selectivity alpha(He/N2) of 6.2 at 115 degreesC, although a selectivity lower than 2 was measured for a ZSM-5/alphaAl(2)O(3) membrane in similar conditions. (C) 2003 Elsevier Science B.V. All rights reserved.