The present invention relates to inhibitors of antithrombin III and the medical use thereof in treating or preventing bleeding. The inhibitors are preferably used in subjects suffering from an acquired or genetic bleeding disorder, such as haemophilia, or in a subjects having a clinical condition characterised by excessive bleeding, such as surgery, trauma and internal bleeding. The inhibitor of antithrombin III can e.g. a peptide, an aptamer or an antibody or antibody fragment that specifically binds to and inhibits antithrombin III.