The aim of the study was elucidation of hemostatic effects of low-molecular heparin Flaxiparin in patients with primary pulmonary hypertension (PPH). 10 PPH patients (mean age 39.0 (+)- 3.2 years, mean history of the disease 5.1 (+)- 0.9 years) were treated up to 6 months. For the first month Flaxiparin was injected in therapeutic doses 15,000 AXa ICU, twice a day. The next 5 months prophylactic doses were administered twice a day (7,500 AXa ICU). D-dimer, fragment 1 + 2, complex thrombin-antithrombin, beta-thromboglobulin, protein C, antithrombin III, antigen of tissue plasminogen activator and inhibitor of tissue plasminogen activator of type I, activity of the latter were measured before the treatment, after the therapeutic and prophylactic courses, 6 months after the treatment. Initially, the patients had procoagulative hemostatic disorders. i.e. activation of blood coagulation; fibrinolytic system was also affected. In the course of Flaxiparin therapy blood coagulation and fibrinolysis improved significantly. However, the effect was not persistent after the drug discontinuation. Flaxiparin can be recommended for treatment of PPH.