This paper presents an overview of investigations of blood coagulation of man exposed to hypoxic hypoxia or hypoxia combined with hypercapnia. Blood coagulation changes were related to the level of hypoxia and correlated with variations in blood gases and acid-base characteristics. Prognostic criteria associated with increased coagulation in response to hypoxia were formulated. It was found that hypoxia of any degree reduced significantly the stimulation effect of epinephrine on blood coagulation and fibrinolysis. The paper discusses the relationship between respiratory and hemostatic functions of blood and mechanisms regulating its aggregation during hypoxia of various degree. It is recommended to add carbon dioxide in moderate concentrations to the hypoxic environment in order to prevent blood hypercoagulation and to increase its resistance to acute hypoxia and epinephrine-induced lesions. It is concluded that the functional state of the blood coagulation system is controlled by the concentration and proportion of oxygen and carbon dioxide, i. e. biologically active gases, in inhaled air and blood.