Growth of silicalite membranes inside the pores of alpha-Al2O3 support tubes was carried out at 95 degreesC. The support tubes had a 1-mum mean pore diameter and were seeded by impregnation in a suspension of 0.1-mum silicalite particles prior to membrane growth. The membranes were weighed to determine the total reaction product and examined by SEM and EDS to estimate the spatial distribution. Reaction product was found at a depth of 100 mum or more inside the pores of the support. The membranes were tested in single gas permeations of hydrogen, nitrogen, h-butane, and isobutane and in the separation of n-butane/isobutane mixtures. After three growth periods, mixture measurements gave n-butane permeances of 10-17 MPU [1 MPU = 10(-8) mol/(m(2) s Pa)] and n-butane/isobutane selectivities of 30-40 at room temperature. The selectivity results are discussed in terms of gaps between the intrapore crystals.