MFI polycrystalline films were prepared on non-porous glass as well as on porous alumina substrates, using secondary growth of seed layers. The secondary growth procedure consists of deposition of MFI microcrystals from a colloidal suspension on the substrate to form seed layers, followed by hydrothermal growth of the seed crystals to form a film. In situ growth was also employed on non-porous substrates that were seed free. The two different growth procedures were compared and it was found that the presence of the seed layers affects film growth and final microstructure. The films upon secondary growth exhibit columnar grain microstructure. Depending on the secondary growth conditions the grains of the polycrystalline films may exhibit c- or [h0h]-out-of-plane orientation. We report single-component and binary permeation measurements using Na-2, SF6 and butane isomers, for MFI membranes prepared by secondary growth on porous alumina substrates. The Na-2:SF6 single-component selectivity is 8-10, while the permeation flux of n-C4H10 and the n-C4H10:i-C4H10 flux ratio from 50/50 mixtures at 22 degrees C is in the range 1.5-5.5 x 10(-3) mol m(-2) s(-1) and 28-62, respectively. The n-C4H10:i-C4H10 flux ratio remains high up to 150 degrees C but decreases drastically at higher temperatures.