1. The authors observed NPY-positive fibers in the CA4 area of the hippocampus from schizophrenics and normal controls using immunohistochemical techniques. 2. Positive fibers followed a straight course and were oriented to exit the CA4 region of hippocampus in normal controls. 3. Many NPY-positive fibers in the CA4 area appeared coiled or helix-like or appeared wasted and thread-like in schizophrenic brains, compared to those of normal controls. 4. These findings may indicate a dysfunction of the interneuron in the schizophrenic brain and support the hypothesis of developmental impairments of the CNS in schizophrenia, and these morphological changes in fibers may relate to schizophrenic symptoms such as memory or/and learning deterioration.