A protease for activating the blood clotting factor VII is described, which (a) is inhibited by the presence of aprotinin, (b) is increased in its activity by calcium ions and/or heparin or heparin-related substances, and (c) in SDS-PAGE, on subsequent staining in the non-reduced state, comprises one or more bands in the molecular weight range from 50 to 75 kDa; and in SDS-PAGE, on subsequent staining in the reduced state, comprises a band at 40 to 55 kDa, one or more bands in the molecular weight range from 10 to 35 kDa, and a band, which corresponds to a proenzyme, in the molecular weight range between 60 and 65 kDa.