The invention relates to novel prothrombin mutants or derivatives thereof having one or more changes in the protein sequence as against the natural protein, are either inactive or have an activity of 10 % at the most and preferably no more than 0.25 % of the natural protein and have a bonding capacity to natural ligands (natural or artificial anticoagulants) essentially corresponding to that of the natural protein. The description also relates to the use of mutated prothrombin mutants or derivatives as pharmaceutical preparations.
