The discovery of enzymes, other than kallikreins, which release kinins from blood plasma was made by Rocha e Silva et al. (1949a) when they observed the formation of bradykinin by adding either trypsin or Bothrops jararaca venom to plasma globulins One year later Beraldo (1950a, b) reported the kininliberating activity of fibrinolysin (plasmin), when it was incubated with plasma globulins precipitated by half saturation with ammonium sulfate. A cysteineactivated protease secreted by Clostridium histolyticum was next shown to release from fraction IV-4 of bovine plasma a bradykinin-like polypeptide (J L Prado et al., 1956). This group of kinin-releasing enzymes, kininogenases, has been growing up to the present time and now includes several proteolytic enzymes.