We prepared bicontinuous composite membranes comprising zeolite A particles. The particles form a monolayer which is embedded in a polymer sheet in such a way that each particle penetrates both surfaces of the polymer sheet. Preparation was done via "float casting"; a mixture of hydrophobized zeolite particles and an appropriate volume of a nonvolatile polymerizable organic liquid monomer was applied onto a water surface. The monomer was solidified via photopolymerization to form the above-mentioned membrane. In as-prepared state (without extensive drying), this membrane is permeable for water vapor (in case of zeolite 4A permeance = 8 x 10(-9) mol m(-2) s(-1) Pa-1, permeability = 1.65 x 1 mol m(-1) s(-1) Pa-1 = 49 barrer) but impermeable for nitrogen (permeance below detection limit of 5 x 10(-12) mol m(-2) s(-1) Pa-1, permeability below detection limit of 1 x 10(-17) mol m(-1) s(-1) Pa-1 = 0.03 barrer). The permeance for water vapor increases with increasing pore size of the zeolite (in case of zeolite SA, all other parameters being unchanged, permeance = 12 x 10(-9) mol m(-2) s(-1) Pa-1, permeability = 2.4 x 10(-14) mol m(-1) s(-1) Pa-1 = 72 barrer). These observations indicate that the water molecules are predominantly transported through the zeolite channels and at the same time block the passage of other molecules. The impermeability for nitrogen in as-prepared state indicates a low amount of defects that are not blocked by water. Furthermore, the composite nature of the membrane gives rise to a reduced brittleness; membranes can be handled manually without support structure and thus might be promising candidates for separation technology.