The levels of automatically measured D-dimer in patients with various diseases were compared with those of fibrin degradation products (FDP). This assay was based on the absorbance changes in aggregations between D-dimer and latex granules coated with monoclonal antibodies against D-dimer. Patients with thrombotic diseases, malignancies, disseminated intravascular coagulation (DIC) and so on showed high levels of D-dimer measured by this assay. Furthermore, the levels of D-dimer were changed in correlation with fibrinopeptide A, the thrombin antithrombin III complex and the plasmin α2-plasmin inhibitor complex during treatment for DIC. The correlation cofficient was 0.768 between the levels of D-dimer and FDP in 572 samples (p<0.001) (Fig. 1). In 337 samples that showed levels of FDP exceeding 10μg/ml, 39 samples in 33 cases showed a D-dimer/FDP proportion of less than 0.15. In these patients, it was considered that the high levels of FDP were the result of increasing fibrinolysis activation more than coagulation (Table 1) or of fibrinogenolysis (Table 2).