To show whether direct proteolysis of coagulation factors may play a role in patients with so-called consumption coagulopathy, granulocytic neutral proteases in the plasma of patients with acute myelocytic leukemia and septicemia were assayed by 1- and 2-dimensional Laurell electrophoresis. Complexes between serum .alpha.1-antitrypsin and elastase-like granulocytic protease could be demonstrated in those patients with acute myelocytic leukemia and septicemia who also had moderate or severe coagulation defects. Despite the presence of a high antiprotease potential, addition of the elastase-like enzyme to normal plasma resulted in coagulation defects in vitro comparable to those seen in the patients. These results and the ability of the elastase-like protease to destroy isolated clotting factors suggested that in certain types of coagulation factor deficiencies, direct proteolysis rather than consumption of clotting factors due to disseminated intravascular coagulation may be operational.