Hypercoagulability and disseminated intravascularcoagulation (DIC) are characterized by the presenceof circulating fibrin monomer complexes in plasma.In342 patients with possible DIC fibrin monomers, fibrinogen, reptilase time, antithrombin III and othercoagulation parameters were determined at frequent intervals.Testing of soluble fibrin monomer complexeswas performed using a sensitive and reliable haemagglut- ination assay, with red cells sensitized by fibrin monomers (FM-Test) and the ethanol gelation test(EGT). Method comparison regarding the influence offibrinogen levels and fibrin degradation products shows that high fibrinogen levels lead to false positive results with EGT. The same effect is observed forfibrin degradation products and EGT whereas no influence of fibrinogen level and fibrin degradation products on the FM-Test occurs.It could be shown that with normal fibrinogen concentrations (200-400 mg/dl) the positive test results by FMT and EGT are comparable, whereas with fibrinogen concentrations below 200 mg/dl the number of positive results obtained with the EGT amounted to half the number given by FMT. In the case of fibrinogen concentrations above 400 mg/dl, positive results obtained with EGT were 3.3 times higher than FMT. Nearlyidentical results were obtained by comparing the influence of degradation products. In case of high degradation product concentrations, EGT gives 4.5 timesmore positive results than FMT.Further we compared the number of positive test results obtained by the FMT with the level of AT III because it is wellknown that the AT IIIHevel decreases caused by proteolytic activity generated in DIC.In this study it could be shown that fibrin monomer increases in parallel with the decrease of AT III. Thiseffect does not occur with fibrin degradation products.