Serial recordings were made in high spinal cats within and in the immediate vicinity of ‘unresponsive’ (presumably glia) cells before and after the i.v. administration of thiopental, pentobarbital, or diphenylhydantoin. After administration of any of the 3 drugs, extracellular sustained potential (SP) shifts and the depolarizing membrane potential shifts of unresponsive cells evoked by repetitive stimulation of afferent nerves were depressed to an approximately equal degree. The results are compatible with the following hypotheses: (1) that the suppression of SP shifts by general depressant drugs is the secondary consequence of reduced neural activity; (2) that glial depolarization is the major source of evoked extracellular SP shifts in the unanaesthetized cord; (3) that diphenylhydantoin has a direct depressant action on spinal neurones or synapses, independent of post-tetanic potentiation and unrelated to activation of cerebellar Purkinje cells.