Members of the G protein-linked receptor superfamily have not yet yielded to X-ray crystallography. However, diffraction data from other membrane-bound receptors - the photosynthetic reaction centre and bacteriorhodopsin-have provided some information that may also apply to the G protein family. John Findlay and Elias Eliopoulos integrate this information together with analysis of amino acid sequences from cloned receptors, to derive workable three-dimensional models of these proteins. Such models identify ligand-binding and G protein-associating domains.