The invention relates to new prothrombin mutants or derivatives thereof which comprise one or more changes in their protein sequence as compared to natural protein, are either inactive or have an activity of approximately 10% at the most, preferably approximately 0.25% at the most, of the natural protein and which have a binding capacity relative to natural ligands (natural or synthetic anticoagulants) substantially corresponding to that of the natural protein. Furthermore, the use of mutated prothrombin mutants or derivatives, respectively, as pharmaceutical preparations is described.