The ultrastructural studies of QUIN-injected rat hippocampus were performed in long-term experiment in order to determine delayed neurotoxic effect of this compound. QUIN, in a single dose, was administered stereotaxically into the dorsal hippocampus. The morphological changes were characterized by marked atrophy of neuropil accompanied by remarkable glial pathology. The neuronal changes consisted in loss of many nerve cells, abnormalities of nuclear chromatin in the persisting pyramidal neurons and degeneration of postsynaptic dendrites. The glial changes were represented by electron-lucency of astrocytic cytoplasm and their processes. The mechanism of this reaction is unclear and the suggestion, that electron-lucent astrocytes represent a form of transformed glia especially sensitive to amino acids, releasing from degenerating neurons is discussed.