The cerebral ODC/polyamine system is disturbed by brain injury. The main modifications are important increases in ODC activity and putrescine concentration, with minor variations in spermidine and spermine concentrations. A great diversity of stimuli such as cerebral ischemia or overstimulation of the central nervous system by chemical or nonchemical agents can induce polyamine disturbances. Both the contribution of polyamines to the brain damage and their involvement in the repair mechanisms triggered after brain insults have been proposed.