Objectives: Investigation of the blood compatibility requires a number of sensitive assays to quantify the activation of the blood protein cascades and cells induced by biomaterials. A global assay measuring the blood compatibility of biomaterials could be a valuable tool in such regard. In this study, we investigated whether an enzyme-linked immunosorbent assay (ELISA), that specifically measures the electrophoretic "fast form" of α2-macroglobulin (F-α2M), could be a sensitive and global marker for activation of calcium dependent and in-dependent proteases in plasma exposed to biomaterials in vitro. Methods: A F-α2M specific monoclonal antibody was generated and applied in an ELISA setup. Using the F-α2M ELISA, we investigated activation of calcium dependent and in-dependent proteases by polyvinylchloride (n=10), polytetrafluoroethylene (n=10) and silicone (n=10) tubings as well as glass tubes (n=10). Results: We found that F-α2M is a sensitive marker for activation of both calcium dependent and in-dependent proteases. A significant difference between F-α2M concentrations in the control sample and plasma exposed to the artificial surfaces was found (p >0.001). This was observed both in the presence and absence of calcium. Furthermore, the highest F-α2M concentration was in both cases found in plasma incubated with glass. Conclusions: Our findings demonstrate that F-α2M is a sensitive marker for detection of protease activation in plasma by artificial surfaces. Potentially, levels of F-α2M could be a global marker of the blood compatibility of biomaterials.