The contractile activity of blood clots was substantially reduced compared to the blood of healthy subjects. Correlations between hemostatic and contractile parameters suggest that the reduced clot contraction in stroke is due to the lower platelet count and impaired platelet functionality, higher levels of fibrinogen and antithrombin III as well as higher hematocrit and hemoglobin contents, leukocytosis, and changes in the biochemical blood composition. The results show that the reduced ability of clots may be a novel pathogenic mechanism that aggravates the course and outcomes of IS.