Storage of information in single crystals using F-centre coloration has been investigated. The creation of F centres by ultra-violet irradiation in the β-band region of potassium iodide has been used to record an array of 8 μm squares on a crystal surface, with a resolution of about 2 μm. Coloration was confined to the crystal surface by working at a temperature at which the exciton absorption in the β-band region is very high. In a second experiment the reduced image of a microfilm was recorded by optical bleaching of a previously coloured crystal, also with a resolution of 2 μm. Application to computer storage is suggested.