A procedure for wet-proofing Pt/silicalite catalysts with polytetrafluoroethylene fibres is described. The procedure yielded catalysts with stable and high activities for the exchange of hydrogen isotopes between liquid water and hydrogen gas. Characterization of the catalysts by hydrogen chemisorption and scanning electron microscopy showed that the wet-proofing procedure can produce catalysts in which most of the Pt surface in the Pt/silicalite before wet-proofing can remain accessible. Hydrogen chemisorption was found to be a valuable tool for prescreening of wet-proofed catalysts.