The purpose of this study was to determine levels of leucocyte elastase and cathepsin G in the plasma of patients in various pathological states, in which plasma increases or decreases in coagulation and fibrinolytic factors were seen. Simple methods were developed to measure the leucocyte proteinases and the results were correlated with conventional assays of coagulation and fibrinolytic factors. The total number of patients and total number of plasma samples examined were 340 and 1292, respectively. No correlation was observed between the plasma levels of elastase and cathepsin G, and plasminogen, fibrinogen and leucocyte counts. There was a weak overall correlation, however, between the leucocyte proteinases and each of the four parameters: D-dimer, thrombomodulin, antithrombin III and platelet count. There was a strong correlation between leucocyte proteinases and D-dimer and thrombomodulin in those patients with plasminogen levels within the normal range. Increased D-dimer levels, as well as plasmin, may suggest that elevated leucocyte proteinases contribute to elevated fibrinolytic mechanisms in these instances.