THE synthesis of inorganic mesoporous materials using ionic surfactant template molecules was first reported in 1992(1,2), and surfactant-mediated synthesis has since been used to form a variety of mesoporous materials(3-8). Such materials could find application in catalysis, membrane and separation technology, and molecular engineering. Previous syntheses have used low surfactant concentrations, and the templating mechanism (which is still controversial) is thought to be a cooperative process involving the interaction of inorganic ions vith discrete surfactant aggregates(1,2,5,9). Here we report the templating of silica mesostructures from ordered liquid-crystalline mesophases : the resulting silica phase, with pores of similar to 3 nm diameter, is a cast of the organic mesophase. As the phase diagram of the surfactant/silica/water system at high surfactant concentration is similar to the (known) phase diagram of surfactant/water alone, this approach should introduce an element of predictability into the synthesis of mesoporous materials.