In this experimental work, the acetic acid steam reforming reaction for producing pure hydrogen was studied in a Pd-Ag dense membrane reactor (MR). Two kinds of catalytic bed patterns have been considered: in the first pattern a Ni-based commercial catalyst has been packed inside the membrane lumen while, in the second one both a Ru-based and a Ni-based commercial catalysts have been packed together in the membrane lumen. The experimental tests have been performed in the temperature range 400-450 degrees C and in the pressure range 1.5-2.5 bar. The results are reported in terms of acetic acid conversion, hydrogen recovery and products selectivities. It has been found that the MR is able to give a rather high acetic acid conversion with a 30-35% hydrogen recovery. Moreover, the second catalytic bed pattern is able to increase the hydrogen production and to decrease the methane production with respect to the first pattern. (C) 2007 Elsevier B.V. All rights reserved.