1. The thrombin receptor has now been cloned and found to be a member of the G-protein-coupled seven-transmembrane domain receptor family. 2. The receptor has been detected directly in platelets, endothelial cells and smooth muscle cells and studies using receptor-derived peptides have demonstrated that this receptor may be the one responsible for many of the actions of thrombin in platelets, endothelial cells, smooth muscle cells, fibroblasts, mesangial cells and neural cells. 3. The receptor appears to be activated by the novel mechanism of cleavage by thrombin to yield a new N-terminus which then interacts with the receptor as a tethered ligand to initiate cell activation.