Factors of significance for the release of kinin were estimated in plasma from patients with specific, exogenous allergies and in that from healthy individuals. There was no evidence that the rapid initial kinin release in plasma from allergic patients caused by submaximum concentrations of hog pancreas kalikrein or by acetone-activated human plasma (2) was due to an increased level of prekallikrein activator (activated factor XII), to prekallikrein itself or to a factor possibly positioned between active factor XII and prekallikrein. In addition, the rapid halt in kinin release observed for the patient plasma could not be ascribed to an increased level of alpha2-macroglobulin, CI-inactivator or alpha1-antitrypsin. It is suggested that the differences in kinin release registered between the patient plasma and the normal plasma might reflect differences in the relative amounts of kininogen fractions present.