THE synthesis of microporous materials such as aluminosilicates and aluminophosphates, which are widely exploited as solid acid catalysts, ion exchangers and in gas separation, is facilitated by the use of structure-directing agents (often referred to as templates)(1). These are generally organic bases, and are included in an inorganic gel medium so that the microporous framework condenses around them; the final structure of the framework reflects, to differing degrees, the shape of the template. Although there is growing confidence(2) in being able to target a particular microporous structure by adroit choice of structure-directing agent(3-7), no a priori method has been described for generating potential templates for either existing or hypothetical structures. Here we present a method for ne novo design of template molecules, which are computationally ’grown’ in the desired inorganic framework. Our method is successful in generating known templates for existing microporous materials, and a new candidate suggested by this method succeeds as a template for the target material. Our method should be generally applicable to the field of template-directed hydrothermal synthesis of crystals and to other fields of chemistry involving host-guest recognition.