After many experiences with ZSM-5 layers on flat ceramic discs the investigation now was focused on the preparation of ZSM-5 membranes on the inner surface of ceramic tubes and capillaries to get useful membrane shapes with a high membrane area/module volume ratio for industrial applications. The influence of two different types of seeds, the tube diameter and the movement of the synthesis solution during the crystallization step was investigated. By using nanosized MFI seeds and by pumping the synthesis solution through the support tubes homogeneous ZSM-5 membranes of 30 mum thickness and a high H-2 permeance of 45001/(m(2) h bar) and a H-2/SF6 single gas permselectivity above the Knudsen factor were achieved. (C) 2003 Elsevier Science B.V. All rights reserved.