The application of zeolite Y membranes to the potentiometric sensing of heavy metal ions is described. Membranes are prepared from a pressed disk of zeolite Y, treated using tetraethyl orthosilicate (TEOS) as a silica source. The resulting silica-zeolite Y composite membranes are characterized by powder X-ray diffraction, MAS NMR and their potentiometric response to cations with a diameter greater than the zeolite Y pore. The initial response to cadmium (Cd2+) and lead (Pb2+) ions obeys the Nernst equation, including appropriate corrections for non-ideality, although the responses decay over a time-scale of several hours for higher concentration ratios. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.