Most of the G-protein-coupled receptors (GPCRs) in the human genome have been described. Investigation will now shift from discovery to analysis. Like many other genes, those encoding GPCRs are frequently found adjacent to each other in clusters. Duplicated genes often share ligands, signalling pathways and amino acid sequence. But, GPCRs do not have to be adjacent to be similar to each other. Phylogenetic analysis divides Family A GPCRs into many clusters that, more often than not, share similar types of ligands. Communication of these types of data for hundreds of GPCRs requires a robust and accepted nomenclature, Locus Link symbols are suggested.