The acid catalysed hydration of alpha-pinene yields a complex mixture of monoterpenes, alcohols and hydrocarbons. By controlling the reaction variables is possible to make it selective to the terpenic alcohols, namely alpha-terpineol. In this paper the results of the hydration reaction of alpha-pinene catalysed by polydimethylsiloxane (PDMS) membranes filled with zeolite USY, zeolite beta or a surface modified activated carbon, are reported. The reaction is carried out at 50 degrees C, using aqueous acetone as solvent. The activity and selectivity towards alpha-terpineol of the composite membranes are compared with those of the free catalysts. (C) 2000 Elsevier Science B.V. All rights reserved.