Thrombin composition, (A,) that contains a non-covalently bonded inhibitor (I) as stabilizer, is new. Independent claims are also included for the following: (1) preparing a thrombin composition (A') by recovering prothrombin from plasma (or its fraction), activating to thrombin, optionally further processing, purification by hydrophobic interaction chromatography (HIC); and optionally inactivation or removal of viruses; and (2) (A') prepared this way.