Process for determining the perkallikrein content and the partial thromboplastin time of a plasma sample

Process for the simultaneous photometric determination of the prekallikrein content of a plasma sample and the partial thromboplastin time of said sample comprising incubating a plasma sample with a surface activator along with calcium ions and a phospholipid to form a reaction mixture, measuring the extinction of the reaction mixture, adding a chromogenic substrate specific to thrombin to the reaction mixture, measuring an optically determinable group liberated from the chromogenic substrate in the reaction mixture by measuring the extinction of the reaction mixture at short time intervals or continuously, said incubation taking place at a temperature of from 20.degree. to 40.degree. C., and simultaneously determining a gradient of a linear part of a curve obtained by plotting time against the extinction of the reaction mixture as a measure of the prekallikrein content of the plasma sample and the partial thromboplastin time by measuring the time it takes the extinction of the reaction mixture to reach a predetermined level.