Factors II, V, X, VIII, thrombin time, platelet count and the thrombelastogram were estimated in 58 persons who had suffered cerebrocranial injuries of varying degree of severity. The aim of the investigation was to elucidate whether and to what extent the injury affected these parameters and whether the destruction of brain tissue could be regarded as the sole cause of the impairment of the clotting mechanism. First estimations in cases of cerebrocranial trauma uncomplicated by other injuries and in cases of cerebrocranial trauma complicated by moderately severe other injuries showed changes in factors II, V, X, VII as well as a pathological thrombelastogram, viz.: hypercoagulability. More pronounced changes were observed in cases where the cerebrocranial injuries were associated with severe complicating lesions: factors II, V, VII, X and the platelet count were reduced by 50-70 per cent of their normal values. Subsequent estimations carried out over a period of 15 days showed that the clotting mechanism had returned to nearly normal within 6-10 days. The use of heparin for normalizing disturbances of the clotting mechanism in cerebrocranial injuries is discussed.