A simple method for the routine determination of plasminogen using the coagulation time is described. 0.2 ml of plasminogen reagent and 0.1 ml of sample plasma, prediluted 1:200, are incubated for 3 minutes at 37 degrees C. 0.05 ml of diluted test thrombin are then added and the coagulation time is measured. It is converted into percent of normal using a standard curve. The test correlates with an immunological method in healthy probands (r = 0.96). Initial measurements in 160 patients show that knowledge of the plasminogen titre may also be of interest outside the problems of haemostasis.