When fibrin fibers are cleaved, fragments are formed-D-dimers. When determining the content of D-dimers with the help of specific antisera, one can judge to what extent fibrinolysis, but not fibrogenolysis, is expressed in the test blood. The increased content of D-dimer is one of the main markers of activation of the hemostasis system, since it reflects both the formation of fibrin in the blood under study, and its lysis.