We have studied behavioral change in mice persistently infected as neonates with lymphocytic choriomeningitis virus. Open-field, electric shock startle, and locomotor behavior were measured on these persistently infected mice and normal controls when they were 2--6 months of age. The infected mice exhibited significantly greater latency to move in the open-field, were more sensitive to low current electric shock and were slightly less active when tested for 4 days in running wheels. Immunofluorescent examination of adult mouse brain 14 days after the initiation of persistent infection with cyclophosphamide (given 3 days after virus) demonstrated viral antigen in hippocampal and olfactory tissue. Behavioral results were interpreted in terms of direct effects of virus on the brain, perhaps altering certain critical neurophysiologic and neurochemical parameters. The possible relationship between limbic system pathology and human mental disorder is raised.