BACKGROUND: Disseminated intravascular coagulation (DIC) is a clinicopathologic syndrome for widespread intravascular coagulation. DIC occurs when the processes that regulate coagulation break down. Staphylococcal infection is one of the causes of DIC. Staphylococcus aureus produces coagulase that can clot plasma. There are two different tests to detect the coagulase; a tube test for free coagulase and a slide test for bound coagulase or clumping factor. The goal of the present study is to evaluate the characteristics of coagulase in Staphylococcus aureus for establishment of an in-vitro model for DIC. METHODS: Coagulase tests were performed by mixing plasma with two-fold diluted culture broths, culture supernatant and culture filtrates. Coagulase activity was expressed as the reciprocal of the highest dilution titer. Cell pellets treated with normal saline, ethyl alcohol, and aceton were used for the clumping tests. Platelet aggregation tests were conducted using a culture broth and a concentrated culture supernatant. A fibrinogen binding protein was isolated from sonificated bacteria and thus, determined the molecular weight. RESULTS: Coagulase activity was higher in the broth culture than in the culture supernatant and culture filtrate. Coagulase activity decreased after incubation at 37degrees C for 24 hours but culture filtrates were clumped after boiling at 100degrees C for 10 minutes. Alcohol and aceton did not inhibit the clumping test. S. aureus induced platelet aggregation but a concentrated culture filtrate did not induce platelet aggregation. Molecular weight of fibrinogen binding protein was 57 kDa. CONCLUSIONS: It is suggested that the plasma clot was due to free coagulase or a clumping factor. Free coagulase is different from a clumping factor. We concluded that the pathogenesis of DIC in the staphylococcal infection was due to platelet aggregation triggered by a clumping factor or coagulase with other substances.