The variation in time of some blood biochemical parameters was investigated in 100 patients with acute head injury and coma of variable duration, in parallel with the clinical course. The purpose of this study was to establish possible correlations between the severity of the trauma (assessed according to the coma classification proposed by C. Arseni) and the variation of the parameters studied. The results show complex correlations between the biochemical events in the patient and the degree of brain function impairment initially and after some time. Long lasting coma (over 14 days) is associated with complex biochemical alterations representing an additional element for defining the clinical condition.