A two-year-old infant developed an inhibitor to factor V after cardiac surgery, with application of fibrin sealant containing bovine thrombin. Investigation of this inhibitor by means of inhibition experiments and immunoblot analysis revealed that the inhibitor reacted strongly with bovine, but only weakly with human factor V. Plasmapheresis proved effective in increasing factor V levels. This patient provides further evidence that exposure to topical thrombin preparations may lead to the development of inhibitors in the postoperative period that may cause bleeding complications.