This volume contains the proceedings of the EMBO-NATO-CEC Advanced Research Workshop on "Guanine-nucleotide binding proteins. Common structural and functional properties", which was held in Renesse, The Netherlands, August 6-11, 1988. The transmission of information is one of the most important processes in cellular life and involves the most diverse physiological functions. The cellular membrane, as the obligatory target for external signals, harbours complex pathways transducing the signals from the receptors of the external stimuli to the cytoplasmic effector. Heterotrimeric proteins are fundamental components of these pathways. Other proteins that are monomeric may be found associated with the membrane or in soluble form in the cytoplasm, and' can also function in signal transduction. Intracellular transmission of signals may proceed in an analogous fashion, protein synthesis being a well-known example. It is one of the most remarkable and puzzling observations of recent years that all of these proteins share common properties, both functionally and structurally. The ir primary structures show pronounced s imilari ties, in most cases concentrated in the NH2-terminal portion of the molecule. They all bind guanine nucleotides (hence the general name of G-proteins) and are GTPases, a crucial enzymatic activity, since it converts the active complex induced by GTP into the inactive one induced by GDP. Consensus sequences have been ident if ied as responsable for interact ing with the different parts of the guanine nucleotide.