A method of facilitating the crystallisation of a macromolecule comprising the step of adding a mesoporous glass to a crystallisation sample wherein the mesoporous glass comprises pores having diameters between 4 nm and 100 nm and has a surface area of at least 50 m.sup.2/g. A method of facilitating the crystallisation of a macromolecule comprising the step of adding to a crystallisation sample a mesoporous glass of the composition Si0.sub.2; CaO--P.sub.20.sub.5-SiO.sub.2 or Na.sub.20-CaO--P.sub.20.sub.5-SiO.sub.2, wherein each of the Ca, P, Si or Na atoms within the compositions may be substituted with a suitable atom chosen from B, Al, Ti, Mg, or K, and, optionally, the composition may also include heavy elements to enhance X-ray diffraction contrast such as Ag, Au, Cr, Co, Sr, Ba, Pt, Ta or other atom with an atomic number over 20.