Another abnormal fibrinogen--"fibrinogen Hannover"--is reported. As known from most dysfibrinogenemias the clottability is poor, while immunologic test, heat precipitating test and the staphylococcal clumping test give normal fibrinogen concentrations. The clotting time when using thrombin or thrombin like enzymes is prolonged, it can be corrected with high thrombin concentration or thrombin combined with calcium inons, but not with thrombin like enzymes combined with calcium ions. The mild bleeding diathesis was first noted when the patient underwent an operation.