The index of the thrombodynamic potential (I.T.P.) as one of the biological means of controlling the prophylactic effect of sub-cutaneous injections of Calcium Heparinate has been studied in 34 spinal cord injuries during the acute phase. Individual tolerance variations, some of them important, have been noted as well as the necessity of adjusting the doses, according to the time after injury. A biological hypercoagulability has been noted within the first and third month after injury. The interest and the cost of such a method are discussed and further comparative biological investigations, using other methods, have started.