Blood coagulation factor X-a (FXa) and Thrombin are well-known serine proteases often used for processing of recombinant fusion proteins., but because they are purified from bovine blood or other animal sources. there is a risk of pathogenic contaminants in the preparation of the proteases. We report here the characterization of a recombinant serine protease produced in Escherichia coli, which can be used as a specific and efficient alternative to FXa, and Thrombin as processing protease. This recombinant protease is derived from human granzyme B (GrB). The protease is found to be very stable in general. and it performs very well in the cleavage of several different fusion proteins tested and was even found superior to processing by FXa, in two cases. (C) 2004 Elsevier Inc. All rights reserved.