THE synthesis of hollow, nanometre-scale molecular ’container compounds’(1,2) makes possible the creation of localized chemical micro-environments with properties different from those of the bulk phases; such compounds can be used, for example, to encapsulate otherwise unstable molecular species(3). Container compounds have previously been prepared by conventional chemical synthesis(1,2). Here we report the construction of a hollow, roughly spherical supramolecular framework by self-assembly(4-8). The framework, which is similar to 2-5 nm in diameter, is constructed from ten species : four organic ligands held together by six metal ions. It has tetrahedral symmetry, and has a large central void, in which guest molecules can be accommodated. We show that four adamantyl carboxylate ions can be encapsulated within this self-assembling cage.