Components of the plasma proteolytic enzyme systems were studied in 15 multiple trauma patients. There were 9 survivors and 6 fatal cases. All fatal cases had sepsis and/or post traumatic adult respiratory distress syndrome. Within the first day after trauma significantly reduced values were found for plasma prekallikrein (PKK), Hageman factor (HF) and Antithrombin III (AT III). In the survivors these parameters were normalized within the first five days after the injury. In the fatal cases, however, the same parameters remained reduced or declined during the observation period. The fatal cases also revealed a high frequency of positive ethanol gelation tests (EGT), elevated serum fibrin - fibrinogen degradation products (FDP) values and persisting low platelet counts. Analyses of plasma samples from both survivors and fatal cases, fractions by Sephadex G-150 gel filtration, demonstrated alpha 2-macroglobulin - plasma kallikrein complexes. These findings demonstrate activation of the kallikrein-kinin system as a part of pathological plasma proteolysis in multiple trauma patients. Persistent reductions of PKK, HF and AT III combined with positive EGT, elevated FDP values and reduced platelet counts indicate a poor prognosis.