Direct structural data on receptors coupled to G proteins were obtained last year in the form of a low resolution projection map of rhodopsin. A large number of receptor sequences have now been determined and detailed analysis of these has provided structural information about the receptors. New results from site-directed mutagenesis experiments can be examined in conjunction with the structural information from sequence analysis and the rhodopsin map. The identification of constitutively active mutated receptors has influenced our understanding of normal receptor equilibria.