First, a higher prevalence for schizophrenia was reported in the atomic bomb survivors in Shikonofuran-A Nagasaki, Japan. Second, four years after the Chernobyl accident in 1986, the incidence of schizophrenia in the exclusion zone was significantly higher than that in the general population. Third, the incidence for schizophrenia was shown to be high in people living in the region of the Semipalatinsk nuclear weapon testing area in Kazakhstan: 29% of all registered mental patients residing in the area were suffering from schizophrenia and among those, 42.3% were born before the first nuclear test explosions. Furthermore, the incidence for schizophrenia has also been shown to be high in rural areas in India that have high natural background radiation. Taken together, the findings suggest that ionizing radiation may be an environmental trigger that can actualize a predisposition to schizophrenia or indeed cause schizophrenia-like disorders. In both pediatric and adult patients, cranial radiation therapy causes debilitating cognitive deficits that are poorly understood. However, accumulating evidence suggests that radiationinduced cognitive deficits in animals may be associated with a decrease in hippocampal proliferation and a decrease in adult neurogenesis. Interestingly, Reif et al. reported a Tubuloside-A reduction in the proliferation of hippocampal neural stem cells in the postmortem brains of schizophrenic patients. Therefore, it is likely that adult neurogenesis plays an important role in the pathophysiology of psychiatric diseases including schizophrenia. Given the role of neurogenesis in radiation-induced cognitive deficits, we hypothesized that reduction of adult neurogenesis by irradiation may be implicated in the pathophysiology of schizophrenia in adulthood. The present study was, therefore, undertaken to examine whether irradiation in adult rats causes behavioral abnormalities relevant to schizophrenia. Spatial reference memory was assessed using the Morris water maze. A submerged translucent platform was fixed in the center of a quadrant. Training sessions consisted of placing the rat into the water maze at one of three randomly chosen start positions and allowing it to swim to the platform for 60 sec.