Data on the content and localization of the recognition site (exosite) of high-molecular-weight substrates in the thrombin molecule are summarized This site, which binds anionic regions of macromolecules, is shown to be involved in the regulation of thrombin activity. Data on the proteolytic mechanism of platelet receptor activation by thrombin are reported Prospects of biomedical studies of thrombin derivatives as new therapeutic agents and combined courses of thrombolytic therapy as well as possibilities for developing a computer model of thrombin interactions for theoretical and applied purposes are discussed