AT III substitution is indicated in patients with inherited antithrombin III deficiency if these patients suffer acute thrombosis, if they have to be treated surgically and in the case of pregnancy in women with AT III deficiency who have an abortion or thrombosis, as well as during and after delivery. In acquired antithrombin III deficiency such as in patients with liver cirrhosis or the nephrotic syndrome, AT III substitution may be necessary if thrombotic complications occur. AT III substitution has been propagated especially in patients with polytrauma, septicaemia, DIC, acute liver failure and in toxaemia. In AT III substitution initial doses of 1 U/kg body weight are used to reach a 1,5% rise in plasma AT III level. If AT III turnover is normal a rise above 80% of normal should be achieved. If AT III turnover is increased, much higher initial and maintenance doses may be needed to normalize plasma AT III levels and to block DIC.