Solvent-free lipid bilayers were reproducibly formed across 100 mu m apertures in a hydrophilic micromachined silicon support. The bilayers were assembled from mixed phosphatidylcholine/cholesterol monolayers at the air-water interface by the Langmuir-Blodgett method. The presence and longevity of the bilayers were determined by fluorescence microscopy. The bilayer seal impedance was also measured. Such a mass producible device for supporting lipid bilayers is of potential value for biosensor development, for receptor and drug assays, and for biophysical studies of ion channels.