Fibrinogen is a key protein both in 1 degree hemostasis, where it serves as a ligand for platelet thrombus formation and in 2 degrees hemostasis where it serves as a substrate for the proteolytic action of thrombin. The goal of the proposed study is the delineation of structural and functional alterations of fibrinogen in sepsis. Most coagulopathies of sepsis are regarded as manifestations of DIC. Clinical reports and scattered laboratory studies suggest that mechanisms other than microthrombosis may effect coagulation changes in sepsis which mimic DIC. Since these alternative mechanisms may have very different prognostic and therapeutic implications, further characterization should have a significant clinical impact. The specific aims, therefore, are characterization of the structural and functional alteration of fibrinogen in the apparent acquired dysfibrinogenemia of sepsis, and in non-plasmin-mediated proteolysis, both bacterial and leukocyte protease-induced, and demonstration of the frequency with which these "pseudo-DIC" syndromes occur. Accomplishment of these aims will be achieved in two phases. During Phase I the focus will be on the analysis of fibrinogen and derivatives in selected diseases where alterations are fairly well-described. Established diagnostic techniques, as well as newer methods (fibrinogen phosphorylation, FPA, F1+2, thrombin-antithrombin complex, immunoblotting of FDP, ELISA analysis for D-dimer) will be applied to blood samples from these patients. Although many of these techniques have been applied in previous studies, the interrelationship of the structural and functional alterations in many diseases have not been demonstrated. Further, with the benefit of these newer techniques, previous investigations may be reopened and/or reinterpreted. In Phase II, the pathophysiologic insights and technical refinements achieved in Phase I will be applied to a prospective study of hospitalized patients with gram-negative bacteremia. Patients with discrepant coagulable and immunoassayable fibrinogen will be evaluated by fibrinopeptide release, fibrin monomer polymerization, 2-D gel electrophoresis, FXIII crosslinking, sialic acid content. Patient with low fibrinogen and low FDP will be evaluated by immunoblotting for non-plasmin-mediated fibrinolysis. Other evaluations will be dictated by observations made in Phase I. After careful delination of the structural and functional alterations of fibrinogen occurring in sepsis, a more rational basis for design of therapy can evolve.