State of kinin system was studied in blood serum of patients with burns of II, III, IIIb and IV degrees during shock and early toxemia. Content or activity of main components of kinin system (kininogen, kallikreinogen, kallikrein, kininase I (carboxypeptidase N)) were repeatedly estimated at 4-6 hrs intervals; BAEE-esterase and antitryptic activities were also studied within 48-72 hrs after the trauma. At the same period plasminogen and plasmin were estimated in 8 patients. The activation of kinin system in burn shock was demonstrated: content of kininogen was decreased on 30-50% (independently on alteration of total protein in blood serum), the kininase activity was decreased, appearance of free kallikrein was observed and content of kallikreinogen was distinctly lowered already within 10-24 hrs after the trauma. Within 24 hrs after the burn the total decrease of kininogen in circulation accounted for 50-70% of the theoretical content. Fibrinolytic system was also activated during the burn shock. Increase in the antitryptic activity within 30-40 hrs after the trauma, which was previously established, is corroborated; the effect correlated with development of burn intoxication. The data obtained suggest that massive production of free kinins occur apparently within 24-48 hrs after burn.