We report the presence of an specific inhbitor directed against Hageman factor (factor XII) in a male patient who suffered occlusive stroke and showed tomografic evidence of multiple previous brain infarcts. The presence of a lupus anticoagulant was excluded by means of the platelet neutralisation test. The reduction of the fibrinolytic activity in response to thrombosis as a result of factor XII inhibition was demonstrated by the abnormal prolongation of the euglobin lysis time as well as the absence of fibrin degradation products (negative D-dimer assay and ethanol gelation test).