The effect of tetanus toxin injected into one gastrocnemius muscle on the steady state concentration of several amino acids was investigated in spinal cord half segments, spinal roots and dorsal root ganglia of rats. Care was taken to ensure a symmetrical afferent input to the spinal cord and to localize the segment with the highest concentration of tetanus toxin. 2. In the spinal cord segments containing the highest concentration of tetanus toxin the steady state concentration of glycine was higher on the side of the tetanus than on the contralateral control side. Results obtained after intravenous injection of 14C-glycine do not indicate that the higher concentration of glycine on the side of the tetanus was due to a higher uptake of glycine. 3. The results obtained in the spinal cord contradict previous findings of other authors but lend support to the prevailing concept about the action of tetanus toxin in local and general tetanus.
