Abstract: The present invention provides a method for measuring the activity of tested substances utilizing a reconstituted plasma kallikrein-kinin system. A series of enzymatic reactions is started wherein an activation of a blood coagulation factor XII is an initiating reaction. The series of reactions is started in the presence of the tested substance in the reconstituted plasma kallikrein-kinin system. Then, the series of reactions is stopped and the physiologically active substance produced in the reaction series is quantitatively determined. In the activity measuring method of the present invention, the real activity (a promoting or inhibiting ability) of the tested substance against the production of the produced physiologically active substance can be easily, simply, quickly and precisely measured. In the reconstituted plasma kallikrein-kinin reaction system the contaminating other factors are substantially removed.

Abstract: A method of assaying a physiologically active substance, which comprises activating blood coagulation factor XII in plasma in the presence of said physiologically active substance being tested to convert prekallikrein in the plasma into kallikrein, and measuring the activity of kallikrein thus formed.