SUMMARYFollowing long‐term administration of haloperidol, the brains of rabbits were examined by electron microscopy, with special reference to the synaptic changes in the globus pallidus, and compared with the normal materials. After three to five months' intramuscular injections of haloperidol (2 mg/kg/day), irregular windings of the cyto‐plasmic membranes of the axon terminals were observed in the axo‐dendritic and axo‐somatic synapses in the globus pallidus. The animals showed neuroleptic and extrapyra‐midal symptoms throughout the period. These synaptic changes are interpreted as reactive changes induced by the long‐term administration of